Done well it can do what any sci fi does; hold a mirror up to society and explore ideas and concepts in a new and interesting way. I loved Xmen growing up because of the politics and how it explored how a demonised minority can be persecuted, not to mention how powerful people manipulate fear of the other and basically institute a massive surveilance state and bring in something like fascism. It seemed quite relavent around about the first few years of the millenium. Stuff like Alan Moore's watchmen is also good for exploring similar ideas but in a significantly more complex way - for instance the comedian kind of got me reading up on Latin America and Contras. Worldbuilding is also usually pretty interesting too... how the world works when you have actual superheroes etc. I quite liked the worldbuilding in Worm for instance.

There is also the power fantasy aspect. With superhero stuff, you can kinda think about what it'd be like to have that kind of power. Also, at the end of the film or comic, you know that however bad things look they will be resolved. Even if someone gets killed you can be fairly sure they will be back so in that way it is safe I guess?