It's a tool for more comfy clenching plus protection of the mouthpiece from toothmarks being made, but not some extra part to make one's pipe more beautiful.
I found it is really ugly to leave rubber tips on my pipes when I am resting them. So I put them on only right before I smoke and when I expect I would clench that particular pipe for a longer time during that smoke, which I rarely do.
@soymilkisgood
Similar to soymilkisgood, I am not clenching 99% of the time when I smoke, and I've developed my love for really thin bits handcrafted out of ebonite, that one can slide in his mouth without even opening his lips. For me pipe smoking also includes looking at the pipe and talking to the mouthpiece directly, to appreciate how good or how bad a pipe is.