Result would be a arrow heavier than needed, loss of some speed, and potentail tuning issues from the arrow length and the extra mass trying to flex.
If you are a 30 inch draw, shooting a 32 inch shaft, minumal. If you are a 26 draw, probably more tuning issues.
Most archery shops/box-store retailers will cut arrows for $1-$3 a shaft and glue your inserts in for you.
What Centershot said: if the arrow and broadhead fall off of the back of the arrow rest, it gets dicey trying to let down, not cut yourself, not cut a string/cable, or anything else you don't wanted to...kinda like this...