We often have large training sessions and have had issues where more than 50 people have tried to attend. The issue is that if the moderator/lecturer did not get there in time they can be locked out of joining the meeting. I would see that on any VMR the system would reserve 1 or 2 spots for moderator/lecturer (1 if they are the same person, 2 if they are different) if they are setup. That way they can always join and conduct the meeting. When it happens it is very annoying to participants (we normally have multiple sessions but invariably everyone wants to attend the same one).