PostgreSQL created a PostgreSQL user on mac. Is this necessary? I just installed PostgreSQL on a Mac (Mountain Lion) today.

The installer created a mac user PostgreSQL on my machine. After installation, the user still exists. 

My question is that why postgreSQL needs a new user? Can I remove this user? MySQL server does not require such a user being created.

Can someone help?
Usually, the Postgres server process is owned by the accompanying system user (not by root or the installing user), so it only has a limited set of rights, making possible attacks somewhat less dangerous.

Additionally, the Postgres system user is normally used to carry the default privileges to initialize db clusters and access newly created databases without password. But you can change all that, of course.

What MySQL does is hardly relevant to these considerations. It is in no way role model in security related affairs.