I'm not the only person connecting to my machines.

Some applications want to open ports and don't have the server-side infrastructure to punch a hole through NAT. Especially P2P apps and some games.

Sometimes I want to run a small, low-traffic web server from home.

Sometimes I'm connecting to my network from a machine that I don't control and can't install Tailscale on.

Tailscale uses the same range as CGNAT.

https://github.com/tailscale/tailscale/issues/12829

You shouldn't be seeing the CGNAT addresses inside your home network, should you?

Depends on your network, router configuration. But in any case, if you install it on a router where the upstream uses CGNAT yes, you would.

Router straddles inside and outside. I know there's a way where you could put tailscale on your router but it's not the normal way to use it.