Imagine a rollercoaster waiting line. All your family goes enter the line together and join the line in hopes to all be on the same ride. Then its your turn but you realise 5 of you wont make it on the ride, so all your family leaves the queue, then re-enters the queue at he end again. But because you did that, the ride had to start without being full.
Now you have people get thrown in an already started rollercoaster and gettijg shred to pieces on the rails trying to catch one of the free seats while you and your family are doing it again at another line.
The bad thing about queue synch is queue dropping.