Before you happily accept or seek additional teaching activities, be aware of two factors: first, they will eat up a lot of your time, in the beginning it's mainly preparation, but also mentally exhausting.

Second, often the university will not be able to offer you teaching which is directly related to your own research and you might end up in an unpleasant situation (as Jojo described earlier) where you basically have to learn a subject from scratch in order to be able to teach it.

Although sometimes beneficial for PhD studies, my advice is not to do it, unless it helps you to complete your PhD.

I agree, it does eat up a lot of time while you're preparing it. But once you've got the lecture down, it should be relatively smooth sailing.

Having university teaching experience can be a boost to your resume when you're looking for academic postings after your PhD or postdoc.