I used to do that Saša 
and I only ever did clean installs, however over the years, with clean installs becoming more of a pain (mainly for copying your Mail items over) and with upgrades never giving me any problems I felt more confident in upgrades 
Also last time I asked Has anyone upgraded to MacOS Mojave? Did it break anything in your dev environment? - #2 by chrismccord @chrismccord replied first, saying he’d done it with no problems so that further boosted my confidence - I thought if Chris is upgrading so quickly maybe I’m worrying needlessly 
I’m usually tempted by features, admittedly not usually dev related - for instance being able to receive text messages/phones calls on my Mac was pretty cool in the last major update.
Also for Catalina, I like some of their efforts on security (even though I know it may be a pain for dev for a while). I actually ended up migrating my data on to another Mac, then upgrading that, and I was pleasantly surprised by this:
I’ve always hated the idea that programs can access all your files - so who knows what they are uploading in the background? Maybe I am being paranoid but being able to block access to your files like this is a step in the right direction imo. I’d like to see it go further, with perhaps being able to fine-tune folders an app can access along with logs of files apps have accessed and whether they may have uploaded them anywhere.
