The Late Night Sausage Fest.

[Xithras]

13. Many of them still do.

Hosts get sick, take vacations, etc. Most shows still have guest hosts that fill in from time to time. A number of months ago I was watching the Late Late Show when Drew Carey was guest hosting it, and he was as funny as ever. I know that Letterman also had a lot of guest hosts over the years...including Jimmy Fallon. Most shows do it when they need to, but it's not something they try to schedule in.

The Tonight Show was an oddity in that it had consistent permanent guest hosts who stepped in periodically, pretty much whenever Carson wanted a break from the show. That ended when Joan Rivers left, because Carson felt that Rivers had betrayed their friendship and used his show to springboard her own talk show career. After she left, Carson decided that he wasn't going to be "used" again, and ended guest hosting entirely on his show. The Tonight Show didn't have another guest host until Leno took over, and he wasn't really big on guest hosting himself, so it's remained a rare thing ever since.