Teams posts service messages to the General channel to inform people when members join or leave a team or for channel operations. The information can cause problems in some situations, like when organizations go through corporate restructuring and lay people off. The problem is that Teams doesn’t give administrators any way to disable these messages.
Do people read the notifications posted by Teams to the General channel of a team when someone joins or leaves the membership? Maybe they don’t take much notice, but these messages can tell you that someone has joined or left the company. If you think that Teams should have a setting to suppress “add member” messages for a team, consider supporting the User Voice suggestion on the topic.