We have a service contract with a local heating oil company. It includes 1 tune up per year. I asked him a couple of questions and he was nice and answered them. One of the parts he was replacing had stripped threads and he had to wait for the parts truck to deliver a new one, but it’s covered by the service contract.
Right now he’s in his truck, doing paperwork I assume.
For actual machine equipment it’s a good idea to have someone look at all the pieces-parts regularly - they know when something “looks wrong” although that can become the “you need a new this/that” so obviously it varies.
For electronic components I think it’s just an on/off type of situation, I wouldn’t think a “checkup” would do much the system isn’t already doing by itself regularly.