I rarely, if ever, take in my mechanical machines, I service them myself.
I only take in my computerized machines if they are not performing properly. Otherwise, I clean out the bobbin casing after every project and as long as it works fine, I don't take it in. After 20 years of sewing on my computerized Kenmore, I decided it deserved a servicing. When I got it back it wouldn't work properly, I took it back in and the technician sat down with me and we discovered I had worn out the plastic presser foot!! He replaced it and it has been humming along ever since.