An earlier commenter noted that one of the features of Firestore is user-level security, i.e. clients can only access their own data.
This makes sense for many apps in a document-based/NoSQL model, and may let you avoid any need for your own back end.
But it makes less sense when you start introducing relations and data models become more complex.
e.g. pretty soon we'll need to join to a lookup table. That presumably means that that lookup table needs to somehow be opened up to all users, while for other tables the user can only access their own data. Starts getting complex real fast.
This makes sense for many apps in a document-based/NoSQL model, and may let you avoid any need for your own back end.
But it makes less sense when you start introducing relations and data models become more complex.
e.g. pretty soon we'll need to join to a lookup table. That presumably means that that lookup table needs to somehow be opened up to all users, while for other tables the user can only access their own data. Starts getting complex real fast.