It puts an extra key in that area, giving me one more candidate to use as Compose. (Of four laptop designs, I think I’ve used RMenu as Compose on two of them, and RAlt on the other two, which I think have RMenu as Fn+RAlt or Fn+RCtrl, one each. It depends on the positioning of Space to a considerable extent.)

While on the topic of what keys are on the keyboard and while thinking of Fn keys, I really, really, really wish that keyboards would give a key code for Fn+___ for each and every non-modifier key. It’s absurd that such a simple opportunity for good macro-capability is discarded, and you can only use Fn with the few keys (on laptops, commonly around 16–20) the manufacturer deigned to hook up (e.g. Fn+F1 as XF86AudioMute, Fn+F7 as XF86BrightnessUp, Fn+Space as PrintScreen, Fn+Left as Home, that kind of thing) and the rest are just swallowed in the keyboard firmware. How is it that as far as I can tell no one has done such an obvious and obviously useful thing?

I use it all the time in IDEs, File Explorer, Word/Excel/Outlook, basically everywhere there are context menus based on keyboard focus. It reduces the need to use the mouse, in particular for functions that are only available via the context menu and not via a main menu. It can also be quicker because you just press Menu followed by a letter key to invoke the function, and it’s easier on the hands because no modifier keys are involved.

It has saved me many times when the mouse failed. Especially in RDP sessions where the cursor sometimes develops an offset, ie click location is suddenly a fixed number of pixels away from the cursor tip, making it incredibly difficult to click on things.

I also use it every now and then to change things up when I feel the RSI sneaking.