I again stumbled upon that issue (again)…
Just for general interest: the metronome option in the control room is necessary for the fact that cubase lets you choose now individually on which output channel to hear metronome and where not.
In a more complex studio setup, where you have one musician recording and the mixer room it may be essential to hear the click on the headphones (when recording) but to choose not to hear it in the mixer room.
Off course this makes it for smaller homestudios a bit more complex, but that’s the final reason why there are several places to activate the metronome…
So in the main transport bar we activate metronome globally, and if it is active, we can choose in the control room on which output to hear it and where not.