What function does this key do???

[Elite Knight]

As the title says what does this key do??

[fjdhdhcyfhf]

looks like its just there to give you a backlit middle finger

[ARikozuM]

It disables the Win key whenever you'd like. 

 

Edit: Win = Windows key.

[-rascal-]

That is the 'Game Mode' button (older Logitech keyboards, a switch).

 

As mentioned by @ARikozuM, it disables the *Windows* so you don't accidentally tab out of the game, etc.

From the looks of it, the newest revision allows you to pick WHICH keys to disable, too -- you can pick can choose in the software

 

http://support.logitech.com/en_us/article/Activate-Game-Mode-and-disable-keys-on-the-G810-gaming-keyboard?product=a0q31000009uvIEAAY

 

 

 

[Elite Knight]

Thanks that might save me a lot in games when i hit it xD. YAY

[Marcseli]

you can also modify its function in the logitech gaming software. I got the same button in my g610

[mariushm]

it's there to blind you with that annoying blue light