As with Rails, my take is that if you need to make a web app, use the big framework. The pieces you don't use don't cost much in terms of performance or maintainability, but the inverse is true otherwise: piecing together your own Django with a lighter weight framework adds a maintenance overhead that you wouldn't have with a batteries-included framework.

I use Flask for simple APIs and microservices. If I'm writing a full web app, it's Rails (or Django).