When I installed eM Client, I quickly accepted its offer to disable the “online” status notifications so I wouldn’t be interrupted so much. Since doing this, eM Client has caused the computer to make a sound occasionally, but I didn’t know why. I only just realised that this sound was the result of people going online. I already knew about the feature, but I’d figured that since I told eM Client not to notify about this anymore that it wouldn’t still be notifying me.
I think when users accept the offer to disable the status notifications, the corresponding notification sounds should also be disabled. Alternatively, I think the user should at least be either offered a choice about this or told that the sound will still remain.