This glitch allows the Player to get under the map.
You need 2 Persons to do this glitch.
Once you are under the map you can swim anywhere.
When you leave and join the Server you will spawn exacly where you swam (but on the surface).
This can allow you to reach locations you are not suppose to reach (e.g. Die first floor of the Apartment building) or you can glitch into players bases.