Rig Tension

The way I see it you need enough rig tension that the mast stays as bent as you require up to a wind strength that you can handle.  Above that wind strength you want the mast to bend more.  The amount of tension controls (amongst other things) when this change-over occurs.  If you have too little rig tension this change occurs before you are fully powered.  If you have a very flexible boat - such as my old plastic Enterprise - it is noticeable that you can't get enough rig tension to maintain control of the mast in strong winds.  My 4000 on the other hand is very stiff and the rig remains stable in very high winds and hence the other controls such as downhaul and kicker are very good at depowering it without drama.

I'm talking about light winds and strong winds ie when under-powered and over-powered.  There is a third wind strength called a drifter where sensible people retire to the bar, but if you do get caught out you'll find it really doesn't matter what what rig tension you use.  Much better to make sure you catch the puffs.