tags/labels like you are working on project a, b,c. In macOS, you can now tag files, emails, messages, notes with tag_a, tag_b, tag_c for their respective projects and find everything belonging to project a by searching for tag_a.
The Gnome developers refused to add tagging functionality, because it would be ‘confusing’ for user to have more than one way (filesystem) to find things… I mean, if the average Apple user can be trusted to use tags, I see no reason why the average Gnome user would be overwhelmed.