It like until its only 80% full. It is to avoid too many people coming in fighting for those last spots and lagging the server.
Yes that's what my bro said. After the server hits 120 people and gets locked you have to wait until 25 people leave before it will let people join. That's ridiculous. I can see waiting for 5 or 10 people to leave (so people aren't constantly trying to join the server). It's a 120 man server, you shouldn't have to wait until there's 95/120 before it lets people join again...
In all honesty though, if 20 people are trying to connect at once, does it really take up that much network resources on the server that it's unable to handle the requests from people in game? Wouldn't the server receive the request and send back a deny, how many packets can that really be? This is 2012...