When you are a member of a group, you can create new forum topics, that are sticky, while posting in the group activity stream alone is more random. So if you have a specific question in a group, you should create a topic, that is easier to follow and to answer. Also you can create your groups and manage them and invite.
For general questions you can use the Q&A function (https://synthwaver.com/qa/). Tip: It can be used like reddit posts, with the up- and down-vote function.