When to remap keys at the Emacs level vs. the system level?

My approach: start from Emacs unless it's impossible.

• It's necessary to go up to the system level to relocate some keys, namely the modifiers (Shift, Ctrl, Alt, Super) and Caps Lock.
• It's necessary to go up to the system level when you're making a seamless blend between Emacs and a window manager.

What links here

• Keyboard design