The first thing I did when the default changed was to turn transient mark mode off, as quickly as I could.
I had no idea that pressing C-SPC twice would deactivate the display of the active region, and since I have a habit of setting mark quite often (to mark a region for copying but maybe later deciding not to, or to mark a place to return to), I had an almost laughably hysterical reaction to having a highlight that "chased" the cursor around the screen.
It was an almost visceral reaction of disgust: "NO, I didn't tell you to DO THAT, make it STOP".
jcs writes, about turning transient mark mode off:
That strikes me like living without air conditioning. Sure, you can do it but why?
I have never lived with air conditioning and I likely never will. In my part of the world it would be a huge waste of energy for very little gain. I'm sure it is different in different climates.
Anyway, bad analogies aside, as for transient mark mode, I guess it is habit I have developed from using Emacs for many years - I have no problem keeping track of where the region is without having it highlighted, and I enjoy not having to do anything to deactivate the region if I don't need it after all.
The only place it annoys me is in Magit, if I want to add a specific subset of a chunk of a diff, I have to make an active region. It took me quite a while to find out that to do that, I just have to press C-SPC twice, which is okay, as I use the Magit functionality way less often than I do everything else with regions and marks.