In my group, we had an internal newsletter for several months and only posted it on the main wall. The main drawback was that we did not reach our inactive people or people having disabled e-mail notifications as one of our goals was to activate the more inactive ones. Unfortunately, we stopped it due to a lack of resources, mainly time.
For our general assemblies, we as an association are legally forced to invite everybody via letter or e-mail. Therefore, we ask new people to sign up through a form on our website before we let them in on Karrot.
I think it would be nice to have a flexible newsletter/announcement feature in which you could choose to which of the following to include:
active group members
inactive group members
non-members from a list
The latter would be the trickiest to implement with more things to consider, but it can open up some nice possibilities, like for example a button on the group’s public page (/groupPreview) for non-members to sign up for a newsletter.