I would never have gone beyond 10.6.8 except for the fact that some critical software, like Turbotax and iTunes, now require later versions of the OS.
I made a 10.10.3 boot drive which I only use when I have to use software that won’t run on 10.6.8. the ratio is something like 95% 10.6.8 and 5% 10.10.3.
As far as I am concerned, 10.6.8 represented some sort of peak.
I never updated iTunes so mine still works. Apple is becoming more Windows-like in the increasing complexity of “making thing that just work”. My wife and daughter are having a hard time setting up email accounts on their iPhones and my daughters MacBook Pro had to be reset and lost iTunes and iPhoto. Eh. I told them not to upgrade. They never listen that once your machine works just leave it alone.