Personally, I rather err on the side of making a bow "too" long than too short. As long as you keep those tips low-mass, a few inches of extra length only means a sturdier bow. A too short bow means a bow in pieces, or the ever-so-frustrating chrysals showing up after the first layer of finish (gah!).
I don't really have much smart math to figure it out, I sort of look at the stave (crown, knots, "character"), the type of wood, and my desired draw weight and take it from there. Somewhere along, though, I figured that 65-67" ntn is a good length for a pyramid design of medium weight at 28" draw, medium quality wood (elm, ash, juniper). This for a stiff handle (8-10") and 6-8" of stiff tips. For an extra inch of draw length, I add 1,5 inch ntn. For an inch less draw, reduce ntn with 1,5 inch. Parallel limbs half the limb length generally means I can shorten the bow a bit, but then stacking might become an issue so I'll usually add a bit of reflex/recurve to the tips.
But it all depends. I sell bows almost exclusively to folk who shoot at targets on a lawn, not hunters (hunting with bow and arrow is illegal in Sweden). I can certainly see how pushing the wood a little to make the bow shorter is a good thing for a hunter. Also, when you sell bows to people it's sort of bad business to design bows on the limit of what the wood can take. A little redundancy is good.
I think this thing with making bows short is something a bit more common in America than over here. That's just my feeling about it. Maybe euros are more influences by English archery, with their 80"-ers, and Americans more influenced by native american archery? Not sure.
