I can understand what antes bring to a tourney, but why would you have them in regular cash games?
Action is the one word answer!
Antes were common in all higher limit (5/10 and better) Seven Card Stud games, and variants like Eight or Better, and Razz. Very rare in Texas Hold'em games. I also believe that most higher limit five card draw games like lo-ball and jacks or better also commonly had antes.
The downside to Antes are that they slow down the game. It is one more step for the dealer, and to many players always need to be asked for antes further slowing down the game.
The upside to antes is that it makes for a much better action game. It raises the costs of a player for each hand. You cannot profitable play an ante game playing tight. The range of hands you must be willing to call with, raise with and call raises with is much broader. It naturally makes a tight strategy less effective. It changes the whole mathematical dynamic of the game. Pots are larger, overhead is larger, and players have an investment to protect in every hand.