Arrow length is more about spine and draw length. The longer the arrow the lower the spine so if you know your bow likes say 40-45 but your shafts are 50-55 then you can leave them long and effectively lower the spine (there's a rough formula but darned if I've memorized it, lol). Also if you have a long draw length that can be important, for me and my Manchu bow using a thumb ring I have a draw around 32-33", which is a real pain because I have to order 35" arrows and those are kinda hard to find, lol.