Sure. The rationale I had in mind with this was:

1. If UserA is adding UserB to a group, this is an assertion that *UserB* would be interested in the group, but not necessarily UserA and so this might be a lot of non-beneficial noise in the feed. Especially if UserA is an instructor who assembles collaboration groups for their class, for example.
2. If UserA is being added to a group, then it is an assertion that UserA would be interested in that group, so you would want to send to the followers