Is this dependent on which class of boat I'm sailing? Or is it just random? Or wind strength? Or personal preference?

On the beat, default position is with a shelf on the foot, but add more depth for pointing or power by easing, which makes the lower leach stand up.

On the reach, more depth by easing the foot for more power, fetching or close reaching I might  flatten the foot if this makes the boat feel more balanced.

On the run, I am not a great believer in letting the foot off, prefer more projected area of having the sail to the bands, also like to have the top of the sail twisted to the lee, which I think an easier leech will assist.

This is based on the classes that I sail Solos and Salcombe Yawls.  In the Solo the tack inhaul is adjustable, this makes the decision much easier at the windward mark, leave the outhaul set, simply dump the inhaul, then pull it back on at the leeward mark to your preset position ...with no loss of area offwind.

Having it loose on a beat depends on wind strength, in light winds you want to keep the draught small, to maximise contact and flow, and in stronger winds tightening the outhaul reduces power and also reduces drag, so you may have the sail full in medium winds but once you have enough power to have the boat moving fully tightening to reduce drag, and then to reduce power helps. How much power you need will also depend on the sea state. 

The same general principals may apply differently to different classes - and I can't speak for Enterprises, but in my Devon Yawl we tend to have the outhaul tight upwind pretty much regardless of wind strength - though we generally sail on sheltered water, in a chop that might not work best.

However, it's usually quicker to sail with flow over the sail (like Peter says above). For which you want it to be curved. You may have to sail angles to achieve this if the mark is dead down wind, which means gybing if you have stays, or transitioning to be the lee in unstayed boats like your laser. 

However, the out-haul makes very little difference to overall sail shape as long as it is relatively well set. It only effects the shape of the bottom couple of panels and kicker and Cunningham are far more important. The outhaul probably gets unwarranted attention because is is the most visible part of the sail.

In toppers and lasers I would let if off downwind and on reaches. However, if things were hectic at the mark rounding I wouldn't bother as you'll loose ground moving in / forward to get it which you don't want to be doing at critical times (if at all). 

In 49ers and 29ers we set it for the race. It was in a difficult place to get to adjust anyway, but also you're always sailing an apparent close reach. I think we adjusted jib halyard tension more in races than we ever altered the out-haul. 

In the 200 the crew gets it after rounding the windward, just after hoisting. But, if we're under pressure from a boat behind roiling us we'll forget it and focus on getting the kite set and their weight up if needed. We'd only go back and get it if convenient (a lull where the crew goes back in to the boat for instance).

What's needed is two Laser sailors (the same hight weight and build) in identical boats to line up side by side and sail (without kinetics) directly downwind. The onlydifference being that one has tight outhaul and the other very slack...... Any takers?

Calibration is the key ... mark your upwind and downwind settings for your kicker, outhaul, inhaul, cunningham and plate.  This makes it relatively mindless to go to your default upwind and downwind settings, most of which you can set up while you are on the lay to the windward mark, or at a quiet moment on the final run into the leeward mark.  Kicker and plate make the biggest difference, then probably outhaul, cunningham in the boats I sail doesn't make a lot of difference except when you are overpowered.  

If you have got the cunningham on upwind it is vital to dump it offwind, since the compression in the mast bows the mast and depowers the mainsail.

When skin friction is the major drag factor (i.e. in a drifter) plate up does reduce the wetted area quite considerably, as does sitting well forward and heeling to leeward to lift the aft planing sections of the hull clear.

Raking the board only changes the effective chord but I'm with you on up or down, the only time on Raceboards I'd rake was to control railing upwind in a blow. Boats are a bit different I think and, as speeds are usually lower, maybe the effect of rake on balance outweighs the other effects? I'll use half board on the Blaze off wind and lift the daggerboard on the Spice when overpowered to help keep the boat flat.

I think L@sers are impossible to sail without some plate, the Spice certainly is. Plus it if's up much more than halfway you can't gybe as it gets in the way of the kicker (then you capsize).

In every boat with a daggerboard I've lifted it, but for different reasons. In toppers and laser I lift it on reaches and downwind, as you bear away the leeway reduces and you sit in. The leeway is equal to how much you're hiking. So the more you sit in, the higher the plate should be. Having it down just increases skin friction. However, you still need to keep a little down just to enable steerage.

In a skiff you're 'full' hiking pretty much around the course so you leave it down all the time to reduce leeway. 

You can also lift the plate to depower. Having too much plate in the breeze causes the boat to 'trip' up a bit when gusts hit. Plus, as you go faster you don't need as much plate to create the same lift. 

In the 200 with a centreboard, I agree with iGRF. Lifting it changes the section. It also moves the plate backwards in the boat which makes the helm feel funny. You also have to move it back quite far before you appreciably reduce the surface area. All of that has led to me leaving the centre board down in the 200. I know a few people lift it in the very light winds on the run. 

The Spice copes well with full board until you're getting overpowered so I generally set it for the wind strength and leave it unless it changes.

To turn a dinghy downwind, raise the centreboard (pivot the blade backwards) and it's easy to turn downwind as well as acting more like a long keel design.

Just for Rupert - we used to reduce the Firefly death roll by having the crew sit out to leeward, helm to windward and not, emphatically not, to move body position. Ie don't try to keep body upright, roll with the boat. Also, don't try go correct the roll with the rudder! This increased to moment of inertia sufficiently to increase the period of the roll and make it less deadly. Techique was used with the old spoon rudder...

I have found Sail pretty much works with settings used by Laser sailors, especially round our small lake, haven't tried it on long reaches etc, you would get more of a feel of what is happening.

Beating and running, I set it tight enough so you can get your fist between sail and boom.

The problem is it's an untested design, theirs no data from when it was first used, controls on my boat also substantially more powerful than original, larger stiffer boom, centre main instead of off the boom or aft main, wings instead of sliding seat.