Erlang: advantages to separate relx.config?

I always had a rebar.config and a relx.config. However, I read this page by the author of Learn you some Erlang: http://howistart.org/posts/erlang/1/, and he has the relx section in his rebar.config and no relx.config. Is there a pro/con to this? Should I stick them all in one file? What is the best practice for this?

With Rebar3, relx is integrated From Rebar 2.x to Rebar3. Hence, there's no need to have relx.config separately unless you're using relx directly (or with another build tool like erlang.mk).