content-filter with Postfix

[Robert Moskowitz]

I am on Centos 7.

I am reading a lot of different places, including:

/usr/share/doc/amavisd-new-2.10.1/README_FILES/README.postfix

that seem to imply that main.cf should have

content_filter=amavisfeed:[127.0.0.1]:10024

instead of sprinkling it all over master.cf as a -o line.

Does anyone have any knowledge on this?  if in master.cf, which services 
do NOT use amavis?

thank you