It helps on GSM devices, but not so much on CDMA devices. The Incredible is CDMA. You can switch it from 3G (1XEV) to 1X by entering characters (I forget what they are) into the dialer and hitting Send, but there's really no need on CDMA.
The only time, with CDMA devices, that it will help battery life is if you have a weak signal and it keeps switching back and forth between 3G and 1X. Then it definitely helps. None of the switching apps in the market work on CDMA devices, so you have to do it manually.