My brother got this reel of ebay and it didn't come with a manual.  There is a switch with an on/off option. What is that for?  I've noticed when I have it on "on" the clutch comes back up automatically.

Is this all it is for?

Thanks.

Flippin' switch.

It's useful when you're flipping baits because it allows you to pull some line out and quickly re-engage the reel without having to turn the handle

I believe it is use for flipping.  It allows you to cast out and as you let go of the trigger it comes up allowing you to start working your bait without reeling in any access line.  

I just thought is was the Quantum reels that had those.

Or it may be an anti-backlash switch??

Flippin switch!

Flippin switch as mentioned.  Once the thumbar is released the reel is instantly engaged. No need to turn the handle to get it locked in.