I see Caddy as your general use case production web server prior to hitting large scaling needs. I've never gotten it to perform as leanly or scale as well as nginx, but most people will probably not need the headroom nginx provides vs. caddy.

Caddy is significantly easier to manage and get running to a "good enough" stage for people that aren't familiar with nginx and apache, even for most medium sized production deployments.

But, if you've got a team that's comfortable with nginx or apache, and doesn't find themselves spending an undue amount of time fiddling around with managing them, I don't personally believe there's any reason to switch from them to caddy.