Do I have to run "yum clean all" or "yum clean metadata" after adding a new repo file?

Question

I'm reading a few automated scripts written at work, and I'm seeing either yum clean all or yum clean metadata after creating a .repo file in /etc/yum.repos.d for a new repository. Now, I'm automating something for which I'll have to add a new repo file and I'm wondering if this does something other than cleaning the cache and if I should add it, but I don't want to add anything without really understanding what it does.

EDIT: It's suggested even here in this answer: https://superuser.com/a/504109/5184

Solution

Recommended sure is highly recommended

as far as required no..but if you (to use rpmfusion as a example) run :

(inclusion of rpmfusion-free-release.repo)

yum install vlc

WITHOUT at least yum clean metadata it is unlikely that you will get a return.

Reason being that seeing said package in older (pre inclusion) metadata is just not possible.