There are several advantages between short and long risers. Not only is there a difference between the riser itself, but the combination of the riser length and limb length will effect the performance of the bow as well. So it's best to consider both when trying to decide on the length of a riser.
A longer riser generally will give you more of a sight window while shooting. It also will generally be physically heavier, making the bow more stable.
If you compare two bows that are the same and equal in AMO length:
A short riser with longer limbs should be smoother to draw compared to a longer riser and shorter limbs. However, the shorter limbs on the longer riser are most likely faster. The longer limbs will also store more energy depending upon design and draw length.
Answered on 10/29/2013 by Sam from 3Rivers Archery