I would say there is much more maintenance, around schema and migrations. Since there is no enforcement of schema at the database level, you need to be very careful in understanding every single way your application(s) work with the data, and ensure that they are backwards and forward compatible. This generally involves writing a lot of custom tooling batch migration logic and ensuring strict control over code that modifies data.

It's very easy to discover schema migration problems in production as the data is accessed.