I'm not a fan of short arrows after seeing one guy limping across the parking lot and hearing how he forgot to remove his arrow in the dark while decocking his bow. From what I was told he managed to stick about half of a 100 grain thunderhead into his foot just between his big and 2nd toe.
You can kill yourself with a kitchen knife, if you don't pay attention.
Or even easier, with your car ...
But in general, I think shorter arrows have better penetration, since they are stiffer and thus have less longitudinal oscillations on impact. In other words, less bending.
Just watch a a slow-motion video of an arrow from a vertical compound hitting the target.
This bending while penetrating the tissue creates additional friction, and causes loss of momentum.
Vertical archers cannot reduce arrow length, so they play with FOC to reduce this effect.