Purpose of the CODEOWNERS file

[Matthew Pickering]

There have been a flurry of MRs to add ownership to the CODEOWNERS
file but it's not clear to me what this file does.

It links to this page: https://docs.gitlab.com/ee/user/project/code_owners.html

Which explains the syntax quite thoroughly but doesn't as far as I can
see explain how this information is used?

So before I add myself to some files, what does adding ownership actually do?

Cheers,

Matt