The purpose of a Queue is to place a path between the ticket booth and the entrance to the ride. This can fill up very quickly as more visitors arrive than are able to get on a ride at any given time, especially for rides that are more popular by your guests. It is always a good idea to give the queue a little extra room. A couple easy ways to do this is to run it around the outside of the ride, or give it a snake-like design.
Too look at all the variations of Queues in-game, go to Category:Queue