Why do I need a relay for fog lights?

I am replacing the fog lights installed by the previous owner. My 4runner had piaa fog lights wired in by the 2nd owner, the 4th owner (from what I can deduce) removed the piaa fog lights and added their own set of fog lights.

The relay for the piaa fog lights is still in place, but there is currently no relay on the fog light circuit. The current fog light circuit is fuse protected at the positive terminal of the battery, then it is sent to a switch, then the foglights, then back to the negative terminal.

The Hella 450s I bought comes with its own relay, which I'll put where the old PIAA relay is now. Can someone explain why it needs a relay if you can clearly get along without one?

 

It reduces the current flow through the fog light switch.

 

Yep, that's the reason. Older lights with halogen bulbs could draw a lot of amps and switches couldn't handle it.
LED lamps might not draw enough amps to burn up the switch. If you are going to keep it the way it is even for one time out, make sure that fuse by the battery is rated lower than switch. You want the fuse to pop before the switch catches fire and burns down your truck.