I do participate in them because, as some people have said, my views increase when I do. However, I limit the time I spend on them. For example, I belong to three promotion teams. BUT, I only do favorite threads on ONE of those teams each day and I am choosy about what I do.
For my "interest group" teams, such as Etsy Paper, Art and Book Illustrators or my regional teams, I usually do the one or two favoriting threads on each team as these are more within my personal interests and I am happy to fave items for the art related teams.
For those of us who have not yet hit the magic daily sales threshold, self promotion is even more vital than the really successful sales. And for better or worse I suspect these types of things are, in the long run, really important for exposure.
I do other forms of promotion as well--I don't limit it to teams. It's all about what you're willing to do, able to do, and how much time you really have to do things, I think