IOW..using more than required tension = BAD. What? Go30% beyond listed tension reqs for working load on halyard/other lines? 100%? 300%?
Because mainsail draft and depth are controlled by halyard and outhaul (ignoring the effects of vang, traveller and cunningham for now) there is no set tension other than balancing the 2 to create the shape you want. Some guys mark their halyards, first mark up to ten kts, second mark 10 to 15,etc.
Overtensioned is going to reduce draft and move it forward if outhaul tension matches, if outhaul too loose for halyard tension you get a wrinkle (sp?) running from luff to clew.
So, less tension the draft is deeper and farther forward for lighter airs, more tension the opposite to depower the main. You can sail in light airs with a drum tight main, it's just slower because your not getting the most out of the main for the conditions.
I've already committed myself as being more knowledgable than I care too here, as you get used to a boat you develop a feel for what tensions will produce the sail shape you want for conditions.
I'm NOT a sail trim expert but shape is everything, look at the sail, wrinkles, bags, sags means you got something wrong. Draft and shape on main and headsail should be pretty well matched up and balanced.