With this plasmoid you can turn off compositing with one click directly on your desktop. It is for people like me who wish to have a visual indicator for compositing.
The plasmoid is called gamemode, because you mostly need switching off compositing in games anyway.
How it works internally:
It is a qml plasmoid that uses the "executable" plasmaengine to toggle desktop effects via the application qdbus.
The compositing state is polled with a timer. So don't expect that the checkbox will immediately change if you change the compositing state externally (i.e. by pressing Alt + Shift + 12) - the checkbox will however reflect the current state after some minutes.