Media Order list - what is it for?

In the md page heading there is a section Media order:

Does anybody know what this is actually used for - or is it needed?
There seems to be no correlation between images listed and those used in the document.
I use some images in the md folder and some via the image stream.
The Media order list

• does not include all image files in the md file folder
• list files which have been deleted
• includes some but not all image files from the image stream, although they may have been original stored in the local folder
• Does not seem to make a difference if the line is deleted completely.

No really a major issue, just curious.

Did you clear Grav cache?

the media order list in the so called page frontmatter is created or changed when you drag/drop/rearrange image files in the page folder.
plugins like Photoswipe respect this order to show the images in the desired order.
if you just use the folder as an image storage and insert them in your article manually, media order list has no effect.