If cmd + s is not used after the edits and the program is closed then the edits won’t be saved to xmp so next time that file is opened, the edits won’t show on the image/ file.
As written, this is misleading. If you are using LR, you never need to do a Cmd S or Ctrl S - next time you open LR, you always see the edits.
The bolded line should read something like "next time that photo file is opened in another program such as Bridge, the edits won't show"
In LR, xmp is designed mainly for communication with other applications, and LR doesn't create xmp sidecars unless you do something, one or more of :
- enabled the automatic save settings
- done a Cmd S
- exported and chosen Original as the format
It won't create them anything upon import, not unless you enabled the automatic setting. Alternatively you might have used another application such as Bridge / Adobe Camera Raw which saves metadata in xmp files.
But they're just little files cluttering up your folders. No big deal.