I think by services they mean self-hosted, web-based services, or things like sshd - services which work by actively serving connections on a particular port or ports.
And even then, a properly configured SSHD instance wouldn’t really benefit from a firewall, unless you wanted to block all countries besides your own or something.
Linux with no services? That’s not a usable system for anyone who would ask “do I need a firewall”
Systemd is a service that runs logind. What are you doing without them?
I think by services they mean self-hosted, web-based services, or things like sshd - services which work by actively serving connections on a particular port or ports.
And even then, a properly configured SSHD instance wouldn’t really benefit from a firewall, unless you wanted to block all countries besides your own or something.