If a bad guy is close enough for the flashlight's crenelations to be useful, you don't have time be get the flashlight out of your pocket or holster.

I like a crenelated head in order to have an "alternate candle" mode: put the flashlight muzzle-down on a table and use it as an emergency candle if tail-standing isn't a good idea (outdoors, for example).

I do care about beam aesthetics but usually consider other characteristics more important so if it projects a donut then so be it. However, a donut usually means a cheap & sloppy design, and if the manufacturer can't even be bothered to use optics that match the emitter there's not much likely to be done right.