Generally the biggest names are on at the end of the week and seats are scarcest then. It really is a treat to watch. The production is top notch. Jay Leno usually comes out to talk to the audience before the show then they go straight through the program in one take. If you are a jazz buff, the band alone is worth all the hassle.
Situation comedies are a bit different.
There is usually a very funny, very friendly 'warm-up' person to pump up the audience. He also acts as the tour guide explaining the production goings-on during the many interruptions to change sets or reshoot scenes. First season series are the worst. I went to an early Roseanne taping which took 3 hours for a half hour program. The jokes were funny the first time but we deserved actors' wages for laughing on the fourth take.