In my own space, you may see me adjusting a chair’s position, or pushing a book’s spine until it’s flush with the others. This clears cobwebs of connection, reducing my visual clutter. In someone else’s home, I can easily resist, because such adjustments aren’t compulsive, only calming.
Seeing things out of place is like constant background noise of “things that need to be done”. I can better relax and concentrate on other things when the visual or physical “mess” is minimized. Which isn’t to say, knickknacks or bookcases cause me to stress, but rather when there’s something obviously out of place that needs to be taken care of.