I'm glad that's over... The question should be, Why shouldn't I upgrade to the latest OS. Many Mac users I know have sophisticated hardware/software and those companies struggle to stay current. Many users are stuck in High Sierra. Virtually all users of recent Nvidia video cards have no drivers for Mojave, and two photographers who use CAP-1 haven't upgraded.
On the other hand, when my 2009 MP was eliminated for Sierra, I struggled to find the Apple upgrade solution to 2010 (4,1 to 5,1). I regret not doing it as soon as it was available. My final solution wasn't mentioned anywhere I read, and lets just say it failed for the first "FEW" attempts (long story short). Also, while the requirements for Mojave are large, "Metal" video card, APFS, no RAIDs, etc, I have cloned the Mojave boot to HFS+, used RAIDs and it all works with my original GT 120 video card. ????? I don't expect I will have that luck with the next OS, 10.15. I am currently running running both my 4-core and 8-core with the latest version of 10.14.5 with the latest bootROM 144.0.
Both are booting from NVM2 blades with speeds as fast as 2700MB/s. I can also boot either Mojave or High Sierra from a striped RAID on a Sonnet PCI card with dual SSDs (just under 1000MB/s)
My conclusion is to upgrade to the latest OS a short time after it is released. Right now I am just hoping that I will make the 10.15 OS list. The best thing K1K1, is that you know to come to the MacRumors Forum to get the best answers for your Mac. The gracious geniuses who have guided me through my troubles in the last couple years are the best on the web.