[Dovecot] Difference between using auth_realms and setting up virtual mailboxes in postfix?

[Gab IIpop]

Hi, there is a possibility in the future that I might have to support
multiple domain names(but using the same IP address). Postfix has something
called 'virtual mailboxes' to help handle this.

But I also noticed that dovecot has a setting "auth_realms" where I can
specify domains separated by a space.

What is the relationship between the two?