I know of three examples. Toronto is currently home to both the NHL Maple Leafs and the AHL Marlies. It was formerly (2003-04) home to both the Leafs and the AHL Roadrunners. Los Angeles was home to the NBA Lakers and Clippers as well as (2006-2010) the Development League team the D-Fenders.
I can understand how a big enough market can host two major-league teams, but how does it work when one team is minor-league? I suppose tickets are a lot cheaper, but even so I have to wonder how many attend the games and how much media attention they get. Since only one of my examples is current, I have to suspect it’s not an economically sustainable arrangement. Am I missing something?