A faster/lighter arrow will get the target quicker and flatter, but it will also use more energy on impact, therefore slowing down penetration. On deer sized game there is nothing to worry about with most light/fast arrow combo, but some the tougher hide and bigger animals it can result in less penetration and therefore room for error will drop slightly. Now all that being said, I prefer a flatter trajectory, not so concerned about speed. As long as my arrow combo shoots well, the spine is correct & then I match the BH to the critter I am chasing...haven' t any problems to date with this practice.