I think the biggest reason people cut their arrows short is because they are infected with compound mentality and they have to get every bit of speed they can.
yup thats about it, heck i have a friend that shoots full length carbon arrows, 32", out of his wheelie bow. they shoot fine.
on my elb the arrows are all about 3" longer than my draw,my wheelie bow arrows are 2" longer,some 4" longer( for my guillotines
)
shoot what your comfortable with and what flies well
peace,
tim