Hi,
if the acceleration is very low, you will basically just have a slower printer in general, because it will take more time to get the motors up to speed. Even thou its not noticeable much on one layer, it will still add up.
If the acceleration is to high it can cause two problems (which will have similar effects).
Either the Steppers are loosing steps, or the pulley will accelerate so much that it can't grip the belt-teeth everytime. Both events will result in an offset, and the print is ruined.
Hope that helps...