Just........
Something for your passengers to stand on while embarking and dis-embarking
Something to hide the flat spot/damage/etc to your tire(s)
...
I just cannot really think of a good reason for having them.
Aah, you're just jealous because your plane doesn't have any pants! <img src="/ubbthreads/images/graemlins/grin.gif" alt="" />
There were three designs of wheel-pants for the Cessna 150. My plane has the first generation, which are fairly blunt and don't cover as much of the wheel. Plus, they're made of thinner fibreglass (one of the advantages of Clinton Fly-In is you get to compare and contrast). The second generation look like pointy footballs, and the third generation is more blunt, but bigger with little access doors.
The first generation don't weigh as much as later pants (12 vs 18 pounds), plus checking the tire pressure is not as difficult. Finally, I think they look pretty good, which is probably the only real benefit!