I use Lightroom and Photoshop very irregularly. I now can't access Photoshop 5 that was installed on my Macbook because it doesn't work with the current MacOS. So now not only can I not deauthorize the license to free it up for my Windows machine, I can't actually use it either.
I keep older hardware running older OS's for just this reason.
There was one version of Apple's Photos for MacOS that has not been topped in terms of its retouch tool (actually got much, much worse). Since I restore a lot of old scanned-in family photos I keep this aging iMac just for photo editing.
It might be a bit esoteric ... but the Photos that shipped after macOS Sierra introduced a clever new editing view built upon, I think, CoreImage so that it could do all the processing of levels, temperature, etc. extraordinarily fast — leveraging the hardware — for real-time changes as you dragged the sliders.
Unfortunately the retouch tool in Photos for cloning, fixing scratches, etc. took a huge step backward in performance. Like it became unusable.
So simply for dealing with old scanned family photos that have lots of scratches, tears, etc., I have stuck with Sierra Photos on my one machine.
