First, the habit of noting odd ideas or phrases is an old one; many of these would normally have gone into my lyric notebook (and, perhaps unsurprisingly, I have written in there less since starting this). When I was writing more prose, these might have found their way into background descriptions.
Third, I notice that I actively look for phrases to include as I go through my day. As when I joined friends for collaborative poetry projects—a sonnet line exchange, a haiku notebook passed back and forth—the world seems to come alive with details and words. This I love: the reminder that the ability to notice is, more than anything else, a choice. (And whew, does that remind me of the sheer number of chaotic, abandoned writing experiments with which my past is littered.)
I also quite enjoy the way juxtaposition creates new rhythms and ideas as the notes accrete and spread across the wall. As a rule, it's best not to think too much about the origins of a phrase—it should work in its new context without relying on that background information—but I love knowing that mean, in the note at right, was an adjective when I wrote it down and became a verb as soon as it was next to another note. I don't entirely have control over that, and I suspect that the lack of control is good for me. The next step is probably to hand all the notes over to the band and see what new combinations emerge.
Postscript: I just read the NYT piece on creativity, and the footer recommended this one, with its photo of a Post-It wall, from 2014. I don't know what that juxtaposition means either.