I discovered this inadvertently in a 100% run when I did it on a gravity field that was timing out on its own. Basically, if a horizontal gravity field deactivates around the time you're releasing dash, you retain your vertical dash speed. If you hold dash too long, you end up dashing horizontally immediately and don't go anywhere.

I tried to find a place that this actually saves time in level 4 and 5, but since it really doesn't take you very far, I couldn't find anything major. It might cut a few seconds in some spots, but it feels similar to superjump timing, so whether it's worth attempting to line it up -- and risking just falling out of the field if you miss -- who knows.