Approach to creating users in Database

Hi,

what is the usual approach in creating users / role in a postgresql database serving as the data repository to a hosted multi-tenanted application with a large number of users.

the 2 approaches I can think of is

A. The user stays and is controlled only in the application level, the application in turn connects with the postgresql database as a single user name. Any userid to be stored as part of the data is injected by the application

B. Each user is also created in the postgresql database with grant or required rights to the tables.

 

what is the usual practice ?

I am unable to see any benefit in (B) above - i.e. recreating each user in the postgres database 

So what am i missing. A change in approach later can mean a huge rework later