[xemoka]

As a hammerspoon user, probably not if that's all you're using it for. Hammerspoon does add a bunch of extra features mosaic doesn't add—but if you don't need them and you've already invested in software to solve your problem: not likely.

[acmecorps]

If you don't mind, what are the use cases that makes hammerspoon very useful for you?

[xemoka]

Basically the same reason you're using mosaic + the ability to change what exactly is being done. I use it to map 'hyper'+key (where hyper is the equivalent of ctrl+cmd+shift+option and is assigned to control, capslock is assigned to the original control functionality) to move windows between screens and on their own grid. Effectively I just didn't pay for mosaic-like functionality. I have better touch tool, but I never liked having to drag to snap and had hammerspoon implemented already.

[e_proxus]

My use case is to split the screen in two, editor on one side and terminal on the other. I specifically want the terminal to be 80 characters wide (inside that window I use tmux), and the editor to take up the rest of the space.

I've tried most of the simpler, GUI-based window managers for macOS but I haven't found one that let's me set window sizes explicitly in pixels yet. With hammerspoon I figure out the width of the terminal app I want, and adjust the windows accordingly.