That always helps to let people know you are coming up on them. Especially if they are walking or biking or whatever. Last thing anyone needs is for someone to step out in front of you because they did not hear you there right behind them. The bike does make a bit of a whine at speeds but many don't seem to pay attention or notice it.
Ive beeped in stop and go traffic too on occasion, especially if there is a merge or other type of lane shift / convergence, just a friendly reminder, HEY, Im HERE, don't run into me.
Aaron