Capslock is an Escape key for me because I use Vim a lot. I've heard lots of tmux users map it to Control and then configure tmux to use Ctrl+a as the activation mapping, which sounds very useful too.
linux: github.com/alols/xcape windows: github.com/ililim/dual-key-remap mac: karabiner
I use this mapping in my current setup and find it really useful.
Now my capslock is Ctrl. I find that combo to be particularly effective for me.