Like others have said, the most common reason I will use the butt end of the stick (stick flipped over) is for getting a full sounding cross-stick. The second most common situation is when I am playing more aggressive backbeats or just want a consistently bigger sound. This is almost exclusively in my left hand only but on rare occasions I might need to bash a bit and the tips of the sticks won't be as effective in either hand. Like I said, that's rare for me. But since there are some sticks manufactured with only butt ends (mainly for heavy rock stuff) there are certainly those who do that on a regular basis.

IMO, the disadvantage to this method is that it's much more limiting, sound wise. With the tip end being used, you can get many different snare (or even tom) rim shot sounds by increasing or decreasing the length of stick that goes past the drum rim. On cymbals a butt end of a stick is almost one dimensional to me. Having the tip, at different angles, the different parts of the shoulder, etc. available is much more expressive. It's doubtful guys that are mostly bashers would even have that option in mind so it depends where the music lives on whether this makes a difference. 

My .02

Jim