Wow,
For such a simple question??? LOL
Preference is key. Literally, How far do you want the head away from your hand when you draw. As I shoot a drop away, all I have to worry about is missing the shelf when I draw. If I miss the shelf I'm good to go. Also my rest sits way back on the shelf, allowing me shorter arrows. Which for my set up give me better FOC, and KE. and make those little shafts just hummmmmm..
I have my carbons cut to where my heads will just clear the rest by 1/2" or so at full draw. And use the heaviest arrow in the type I shoot ( Easton Axis 340's) that is spined correctly for my draw weight (Right now 75lbs.) ANd I end up with an arrow that weighs 400 grains and is right at 27.25 " long ( shaft only). THen I add everything and end up with a shooting weight of 528 grains. Which then gets spit out of my bow at around 320+FPS... Causing loads and loads of KE way down range. LOL
I could very easily go with a lighter arrow, and probably get them to fly , or maybe even a heavier arrow, ( I'm looking at the full metal jackets,, but dont tell the wife.) LOL. But I have in the past decided through many trial and error sequences, to stick with the correctly spined arrows for my draw weight, and the length I choose to shoot. The " arrow charts" for some reason are not to be taken lightly..LOL>. Much easier to believe them the first time then have to buy another couple of dozen arrows cause you " wanted to try something " LOL
PS dont tel the wife that last part either.....
Thanks Shane