This question comes up often and I take notice that most people don't answer it completely. There are many variables to be considered. Any bow shot at it's max setting will shoot more efficiently and usually more quiet. As for efficiency it's usually a very minimal gain. Whether it will shoot better is a matter of interpretation. Better in what respect?

The bow may or may not shoot faster however. This is one of the variables. Yes it will shoot faster assuming that one can shoot the same weight arrow as at a lower draw weight. But depending on how much the weight is turned up it may be necessary to shoot a stiffer spined arrow which could be heavier in mass weight and thus shoot even slower.

What one will gain is more kinetic energy and resulting momentum to enhance penetration, but here again, how much is needed for the game being hunted and just how much is overkill?

Ohionovice is using a pretty good example of common sense. Don't shoot more weight than you can comfortably and accurately shoot. Bows have limb bolts for a reason. One is to be able to adjust the bow's draw weight to the shooter. Another is as a tuning tool (often overlooked). So what is your definition of "better". Is it to shoot a 70# bow maxed out and struggle with accuracy and stamina or is it to shoot the same bow at 65# and be able to place your shots with precision and confidence even with the bow losing 1.5% of it's efficiency? This is a decision for you to answer to your own satisfaction.