A service is not a look and a nod. On a domestic split it is roughly an hour of work, and it is worth knowing what that hour is spent on so you can tell whether you got one.
Filters come out and get washed or replaced. Both coil faces are combed straight and cleaned properly. The condensate line is flushed and the float switch is tested by actually raising it, not by looking at it.
Then come the numbers: amp draw against the data plate, superheat, subcooling, and the temperature split across the indoor coil. Those get written down, because next spring they are the baseline that shows what has drifted.
Skipping a year rarely breaks anything overnight. It quietly shortens compressor life and pushes your running cost up, month by month, without ever announcing itself.
