by default it just says in the bottom right corner of your screen/vision that you are joining/downloading but for some users it's pretty easy to miss that and become surprised when you suddenly transition/teleport. An option to enable a more pop-up style UI "You are about to join the world worldname" with "OK" & "Cancel" would be nice.
Some people might prefer this over the prior, or vice versa, hence being optional is to be expected.
