I take my one computerized machine in yearly, and sometimes I bring one of my vintage machines, since I never seem to have the time to do my own servicing. Since my service guy is 9 hours(1 way) away, I also have my eye exam, my hair cut scheduled at the same time.

This is what I do. My Bernina's don't tell me when they need servicing and since I have a lot of machines and don't sew on any one of them a great deal, I do every 2 years. When the Bernina was my only machine, I took it in once a year. It did cost me, but it was a top of the line machine and like having your oil changed in your car, I considered it good insurance against larger problems.

I sew a lot so over the years I have taken my machines in yearly for a tune up. I have a 1977 Viking that is still going strong and has been passed on to my daughter. That is a mechanical machine. I have my newer computerized machines also serviced every 12-18 months with me cleaning in between. I service my Featherweights myself.
I think it is important to take care of expensive equipment, just like I do my car.

I take mine in once a year. I have 3 machines to keep in good working order. One thing the service call does is get the lint from deep inside that I cannot reach.

On another note, my friend has the same machine I have (one of them) and she does her own service on it. She will take it apart and clean and oil it. I prefer to have the dealer do that for me. :-)

I have a Sears Kenmore machine from 2010, and I try to get in for maintance once a year. Last year when I took it in the person taking them in said I should just buy a new one, not worth the bother to maintain it. Really?!?!

All my machines are vintage. I have two identical machines that I alternately use, so I can take the other one in for a good cleaning. Basic oiling I handle myself.