This has just occurred to me after being confused about behaviour in vim until I noticed I had Caps Lock on.
On the one hand,
<ctrl>+<shift>+<m> (lower case m) is the same as
<ctrl>+<M> (upper case m), and it's a specific letter and case (M) that triggers a shortcut.
On the other hand, a shortcut "transcends" (for want of a better word) letters and cases, and is more about keys. So pressing
<ctrl>+<shift>+<m> on the keyboard would be expected by a user to produce the same behaviour regardless of whether caps lock is on.
Are there any advantages/disadvantages to each method that you know of?