Nice article. I’ve already thought about switching to includes in my future projects, as my co-worker has trouble reading the long selectors in the dev-tools (i.e. clearfix, which is extended 10 times).
One big advantage of @extend is, however, that you may reuse pure CSS components from external projects without the need of modifying them. As I don’t wanna have some hybrid approach, where i sometimes use @extend and sometimes @include to extend - would it make sense to create an extend mixin like this?