I think it’s the last remnant of a problem that used to be much worse. There were several situations in the past which required the steps you found (moving tracks away from the monitored folder, scanning, moving them back, and scanning again) to fix. Those problems were so common that the process gained a name, the “Plex Dance.”
Most of those issues were fixed, so the Dance is rarely needed anymore, but I’ve found that it is still needed if a file is renamed, or added to an existing album.
