What does "apply all necessary compatibility settings" do?

[RJSawyer]

I have "MS Word 2007-2021 (.docx)" set as my default file format.

When I go to save a file, I often see a dialog box that say:

Do you want to apply all necessary compatibility settings to make this document compatible with the latest version of Microsoft Word?

[ ] Do not show this warning again

Yes / No

But I can't find anything in the PDF manual or online that explains precisely what compatibility settings are changed if I select this. Help, please!

Also, if I select the "Do not show this warning again" box, will TextMaker default in future to applying the compatibility settings or to not appying them? Or will it simply default to applying them if I select "Yes" and to not applying them if I select "No"?

One more question: I have to share documents with a user who still uses Word 2007. Will choosing "Yes" give him any problems?

Thank you!