I am on 39 teams... which may be too many at the moment, for me, anyways.
I've chosen some teams that I can learn from (fro example, this one, and a team that discusses SEO's, seeing as I had no clue what that stood for).
I am also relatively new to Etsy, so I have also chosen some teams that I can post some of my Items on.
One of the benefits that I have found, is getting your name out there. a lot of people who own Etsy shops, also buy on Etsy, so it's great to connect with others.
Hope this helps a little bit :)