If you're using SRAM, sure!

Just kidding, however my Rival does shift fine under load.

I don't race, therefore I don't really need to sprint. However, I think the best thing to do is to make sure you're in the right gear from the beginning. If you do have to shift you can probably shift under load if you have a decent group set. If you're not sure you can do it without messing up, in your head, compare how much time you'd lose if you didn't shift and just pedaled faster to if you were to shift, but if it's not going to be smooth.

If you are over-geared, it's probably best to shift down to get in the right cadence. You can't sprint in too high of a gear, but you can definitely spin up to speed in a lower gear.