Have options.
If the meeting is taking place in a actual conference room, then you should not be able to too book it because you normally can't split a room.
have another option called individual where people are accessing from their desktops with no scheduling needs.
we need to limit room usage, not webmeeting usage. we have had a product training going on and hr tried to do a performance review at the same time, but since there is no resource availability nobody knew two meeting were scheduled for the same conference room. We do have resource rooms in outlook/exchange, but that means you end up with two meeting makers, one from 3cx for the meeting and another manually created one to book the room.