a back up question

Are there rules for thumb for deciding when you can dump a whole database and when you’d be better off dumping groups of tables? I have a database that has around 100 tables, some of them quite large, and right now the data directory is well over 100GB. My hunch is that I should divide and conquer, but I don’t have a clear sense of what counts as  “too big” these days. Nor do I have a clear sense of whether the constraints have to do with overall size, the number of tables, or machine memory (my machine has 32GB of memory).

Is 10GB a good practical limit to keep in mind?