Read the title. I've been meaning to ask this alot but I always thought i'd be thought of as a dumbass...

A switch has two properites, Set or Cleared, and you can detect which one it is at, so basically, it's either 0 or 1, on or off, true or false.

So, basically its a 0/1 command like in most forms of gamescript?

You could say that... the game reads it as on/off (0/1). Cleared = Off. You can also randomize and toggle a switch. When you randomize it, it randomly picks (50/50) cleared or off for the switch. Then it gets really confusing in the number of combinations possible

Switches themselves do nothing.
But you can check for them in conditions.
There are only 2 settings: cleared = 0 (default) and set = 1.
Now you can make logical dependencies between triggers.

EDIT: Sorry for posting info already said, i wrote this, then got disturbed and now i came back to finish without checking for updates

Cleared and set aren't neccessarily on and off. But, it helps to assoiate them with on and off, like most do.

The triggers can read cleared, just as they do set. But, we can call them on and off because they all start cleared, or "off".

In the most technical sense possible, they are.

They are essentially Starcraft's only dedicated variables (other potential vars do other stuff), and are of the type boolean.

They can be Reallly really handy.
(theyre not just in the conditions, you can set them up in actions.)

They ARE on and off. nothing else. Cleared is just fancy off, and Set is fancy on.
They all start off.

As i was saying, they are really nifty little suckers, and helps alot, either by cutting down a map maker's trigger limit by tons,
or sometimes you need them to have a double condition cue.

lol, but blizz sais in the trigger info that switches are used for prevent a trigger from repeating o_O

Depending on how you use them they can do that - among many other things.