It helps loading times for those with crap connections. While the majority might have 324874327tb broadband lines, theres still a lot with dial up or just generally poor connections.
My sig is useless links, something to tell you I will take on render requests and a useless quote which will change from time to time.
My sig is sort of like a shout out!
I use Master skinnerz skin kits
I've just started uploading skins to LFS Skins Database
And i use Bogey Jammer's Ready to render kit.
Okay: because I love CTRA and I'm a gold licenced racer!
The link, the first somewhat professional skin I made, was based on their car. The Porsche BiTurbo. I contacted them for more info on the car and pics of the roof and stuff. They sent the pics to me, and wanted to see how it all worked out. After that I got free tickets to see them race, I met the drivers personally and was allowed in their pit box. And to thank them for all that, I use their site as a sig.