The help file is there to define functions, if you're looking for examples of ways to use the editor you should have a look at any one of the numerous tutorials spread about the web.
Esentially, if you think a trigger may not be working, you disable it and test. You can then leave it disabled until you find a fix.
Initially on, when off, acts as if the trigger is disabled but it can be enabled mid-game. Possibly used for things like RPGs, where you only want a certain trigger (say a boss battle trigger) to occur after all "the super secret items" are collected. This way it won't respond unless it's time for it too.