At the end of the day, it's your equipment.
You can follow the manufacturers recommendation of Time Frame/# of Dives.
OR
Send them for service when they need them (seats wear out, o-rings, leaks, look nasty, etc)
What I do (all my equipment, not just regs):
I do 99% of my own servicing of my equipment.
I have things I do yearly (9-18months): inspecting every consumable (batteries, O-Rings, Seals, Webbing, Zippers, etc)
I have things I do periodically (especially after/during heavy usage. 3-9months): (IP/Cracking effort on regs, Burn times on batteries, small maintenance, etc)
I have things I do before every day of diving: IP checks, O-rings, Visual on all gear
I have things I do when required: service any equipment that isn't happy ..
The only things I do like clockwork are tanks. I can't get fills if I don't!
I have them staggered by 6 months so half my tanks are up at a time. That way when I'm busy, or inactive and don't check, I still have something I can use and get fills.
To get to your original question, I only service my regs when they need it.
I periodically check the filter. When its way to gunky for my liking, I'll do a full service.
When the adjustment screw is turned nearly all the way in on a second stage, I'll do a full service.
When they look to gunky and dull on the outside, I'll do a full service.
When they aren't working properly, I'll do a full service.
_R