I would say that it depends on the type of system.
We're on our fourth home in 40+ years, and have had different maintenance done, depending on the heating type.
The first (propane, hot air); never had service. Of course, we only lived there four years.
The second (oil, hot water); we had service each year during the four years we owned the home. This was primarily driven by a blow back (explosion) that caused fine soot throughout the basement in the first year. We learned to have the ignitor serviced each heating season to make sure it was cleaned/calibrated.
Our third home had a gas (hot water) boiler system. We had it replaced while we lived there (it was a little over 40 years old) due to the water jacket starting to have leaks. We never had any maintenance done to the old or new boiler during our 15 years there.
Our current system (air/air electric heat pump) get's serviced twice a year, under a maintenance plan that costs me $20/month. In addition to just making sure the sytem is running at peak efficency (I change filters on my own - it's cheaper) I also get a 20% discount on parts and labor (no extra for night/weekend emergency service), if needed. I saved a few $$$ last weekend when I had to have a controller card (stayed on emergency heat) replaced.
BTW, my next door neighbor never has her system checked (same size house) and their electric bill runs about 2x mine - even with only one person living there (we have two). I would attribute it to her system never being checked and losing efficiency (e.g. coolent/freon) over time. It seems like it never turns off during the heating or cooling seasons (the outside unit is across from our garage door, so I hear it every time we leave)...
For $20/month, I'm not going to quibble over what gets done during service. It's worth it just to lube the blower and empty/clean the sump - which I have no desire to do
. I'm provided with a full report of the diagnostics run and the readings taken, but I have yet to bother to find out what the numbers mean. As long as I have heat in the winter and cool breezes in the summer, I (we) are happy
...