Suppose that you want your keyboard to change colors based on what key you have held down, i.e.
If you hold control, or control + alt, or control + shift+ alt, etc., your keyboard would change to a different profile, and upon releasing said keys, it would change back to your original profile.
This can be useful if you are using a program with a ton of key-commands, and would like to see what options you have available when holding a specific set of modifiers, i.e. only the keys you can press to do something will light up
i.e., when holding control + alt, "p", "e", and "u" light up
Also, it would be nice for knowing that you are in caps lock/num lock mode; if you hit the caps/num lock button, then your whole keyboard changes color until you hit caps/num lock again, and then it will return to your original profile
iCue has a feature that allows you to set up a profile changes based on what key you press, and I'm 90% sure they have a "release" setting as well so it will switch back after you're done holding a key;
I would love to see this added to Synapse, especially if you can have different ones for different combinations of macros, i.e. modifier keys such as control + alt + shift, etc.