Purpose of "postgres" Unix user [closed]

Question

To access psql, I have to first login to another Unix account

sudo su - postgres

then I can do

postgres@linux ~ $ psql
psql (9.1.10)
Type "help" for help.

postgres=#

However, I don't understand why the postgres Unix account (when I do sudo su - postgres) is necessary. What's wrong with just running "psql" from my original Unix account?

And do the postgres Unix and command line share the same password?

*I'm pretty new to Linux/postgres, so feel free to give fundamental explanations

EDIT: another question: What's the difference between

postgres=#

and

postgres-#

Answer 1

However, I don't understand why the postgres Unix account (when I do sudo su - postgres) is necessary. What's wrong with just running "psql" from my original Unix account?

And do the postgres Unix and command line share the same password?

The Postgres user can't log in and only reads/writes to whatever it owns, unless you create it or configure your computer otherwise otherwise.

And therein lies the reason for it to be around: security. It's not technically required (as an example, homebrew on OSX will use your own username), but best practice -- especially on a server.