My understanding from a very brief skim of what Microsoft was doing with Copilot is to take screenshots constantly, run image recognition on it, and then make it searchable as text and have the ability to go back and view those screenshots in a timeline. Basically, adding more search without requiring application-level support.

They may also have other things that they want to do, but that was at least one.

EDIT: They specifically called that feature “Recall”, and it was apparently the “flagship” feature of Copilot.