Is it necessary to declare "alias_maps" in the main.cf? t.s.

[Thomas Strike]

With all the problems that I'm having with my Postfix setup, I am taking a 
deeper dive into the meaning of each parameter declaration.
Is it necessary to declare "alias_maps" in the main.cf or does it have a 
default file path that it looks to or does it just not look at alias_maps if not declared?
Thanks, T.S.