Pros and cons of using many schemas in PostgreSQL as opposed to just one?
Obviously, you are dealing with the same tables in each user schema. Have you considered inheritance for this? It can give you the best of both worlds for some use cases. There are also some limitations. You can have a separate schema for each user and still search all user tables at once very conveniently.

Related:


Select rows from table where each row refers to a different schema
Find out which schema based on table values


Other than that, at least granting / revoking privileges has to be mentioned, which is much simpler with separate schemas.