Network Services - Any services that rely on the network to run
Important systemctl options
/etc/systemd/system/[target]/)Disabling the service deletes the symlink, so the unit file itself is not affected, but the service is not loaded at the next boot, when systemd reads /etc/systemd/system.
However, a disabled service can be loaded, and will be started if a service that depends on it is started; enable and disable only configure auto-start behaviour for units, and the state is easily overridden.
A masked service is one whose unit file is a symlink to /dev/null. This makes it "impossible" to load the service, even if it is required by another, enabled service.
When you mask a service, a symlink is created from /etc/systemd/system to /dev/null, leaving the original unit file elsewhere untouched. When you unmask a service the symlink is deleted.