I do everything myself. The frequency is based on an inexact formula that uses miles, moisture exposure, frame material, time since last service, time availability, and enthusiasm. Oh, and although I work hard to avoid it, I think some favoritism is going on.
Sometimes they just tell me they need it.
I also use the excuse to upgrade.
There seems to be at least 2 of our stable that get the treatment every season. Last year was busy.
First, a relative needed a bike for cycling Cycle North Carolina so I bought, overhauled and repaired a well used Marin Point Reyes.
The steel Bianchi with only 2100 miles last year got it because it got 3 solid days of touring in a real tropical storm (Tammy) including a night outdoors in the rain.
My S.O.'s Cannondales' well used 105 group (3500 miles last year/7000 miles total) received serious cosmetic damage in a horiffic crash. This bike also survived the monsoon. My estimation that it needed an overhaul. And in my estimation she needed an upgrade, primarily because her new prowess deserved it. But I admit other motives.
Fortunatley I had a nice one year old Ultegra 9 group with only 2100 miles. Problem was, it was on my Litespeed. Bought a new Ultegra 10 group for the Litespeed. Problem solved!
And finally, I overhauled and repaired my S.O.'s older Trek 820, converting it into a campus commuter.
5 is enough for one season!