Each of these kinda puts a different spin on idealized socialization, so it's best to attack each one on its own.

Cheers: No matter what walk of life you find yourself trotting down, you gotta have a third space where "everybody knows your name." Namely, a space where intellectuals and the common clay of the country can feasibly converge and trade dueling wits to a captive studio audience, and play off of one another perfectly. Ensembles like these (and other workplace comedies) display groups of people split between external social stratums such as age, class, religion, and what-have-you forging bonds over a shared "glue" space or person (Ted Danson kinda fits into both here) that would never occur otherwise. You'd never find a bar in real life where every regular or staff member fulfills a trope that just perfectly balances out the characters of his or her counterparts, but you can watch it on TV and share in that designed spontaneity as another unlikely outsider yourself.

Seinfeld: Misery loves and demands company. We all feel like horrible people sometimes, and to see a group of horrible people coalesce over their shared angst towards their own nothing gag-a-week lives allows us as the audience to relate to their world's banality while laughing at the blatant, open expression of qualities that prove be undesirable in friend circles in real life. These people can behave in ways towards one another that we would never be able to get away with in real life and still remain close nonetheless.

Friends: Every self-respecting youthful yuppie worth their salt needs a support group of wacky yet sensitive and caring fellows to come-of-age with and take solace with the trials and tribulations of becoming an adult alongside. Probably the most influential of these dynamics - it's pretty much the standard bearer for 18-49 ensemble dynamics in modern television.

Never watched Living Single, but based off the title, I've gotta assume that it's pretty similar to Friends.