I am posing this question because I don't see an answer anywhere online, other than for "features". OS for the past 3 versions will get security fixes. So what's the point?
I ask because I have a boss who is posing this question. He sees no reason to update a Mac once in place to any new OS until it's replaced 3 years later. Most everyone in IT cringes at this from a feature and security standpoint but we can't seem to drive the point home.
I am trying to find an article(s) - respectable - that I can link him to - that explain the importance of updating you're OS. Not having 3/4 different MacOS versions floating around that are harder to maintain from a system admin side of things (multiple different patch versions and variants). Etc.
Anyone have any advice or links that would help make my case?
I don't have an article. I spent time as a systems admin, though that's not my job any longer.
I absolutely would not update my OS without some justifiable analysis, especially in a professional setting. Even for personal use, I'm fairly risk averse, and I think it's justifiable given Apple's track record in recent years. Not saying that as a "hater", just a believer of the "if it's not broken..." theory. Even when it comes to incremental updates, I'll let other people do the initial testing and I'm ok being a release or two behind.
In a professional environment it's even more important. Again, if things are working well and there is no real value for new features, then why upgrade if you're still getting security updates?
As an example, I was happy with Sierra, I was on 10.12.6 until HS got to 10.13.5. Moved to High Sierra a few weeks after 10.13.5 was out and started having problems. A notable decrease in stability. I went to 10.13.6 and it wasn't any better, so I did a clean install of 10.14.0 out of desperation, with a plan to go back to 10.12.6 if I couldn't get my issues resolved in Mojave. I'm on 10.14.2 and things are running fantastically, but I'm not likely to move to 10.15 unless there's something pretty good in there, now that things are working great again.
For people who like stability, there's a lot to gain from a conservative update timeline.
So why would you update? You do raise good points for sure. Security updates, and consistency across platforms. There are benefits there, but those are not usually mutually exclusive with a conservative update timeline. As long as the OS is still getting security updates, then I've just seen too many issues, personally and professionally, that would prompt me to be aggressive in that regard. If an update being real features that bring easily demonstrated value, that's a different story. In reality though, that's often not the case. I appreciate the cumulative feature additions from Apple. The ones that stick out more than anything for me are Time Machine and macOS/iOS interop (handoff etc), to me those are worth a gamble. But HEVC support from 6th gen Intel support (with HS) has no value to me on a 2015, for example. As much as Mojave has some nice features in it, I'd still take Sierra over High Sierra. I think there are plenty of reasons to not be too quick to upgrade.
You can't run Sierra on a 2018, but you can keep two or three tiers of hardware/OS version I'm sure.