Sims can spend leisure time attending sports game or concert here and as the theater, provides a cheap (if somewhat slow) way to get the Having a Blast moodlet. It also has weekly events such as the amateur olympics.
This is one of the properties you can partner with and own in The Sims 3.
Stadiums generate the following red map tag in-game, as well as a light blue opportunity map tag.
The stadium hosts sports games and music concerts that Sims can attend (being a rabbit hole, players will not see the game). Going to the stadium can grant moodlets.