Our users find a variety of uses for draw.io. Many don't connect up the diagram at all and use the space more as a whiteboard.
If you click "More Shapes" at the bottom right and select Mockups, then open up the Misc and Text sub-sections of mockups you'll find some colored pins and a post-it note sticky shape.
When voting for features, todos, etc, one technique is to get everyone to write ideas down on sticky notes, put them on a whiteboard. After that you place a limited number of votes to indicate your favorite ideas. Doing this physically on a white board has it's advantages, but if you're remote this can't be done. Doing it electronically means you can produce a PNG or PDF easily to embed elsewhere (you could even automatically parse the XML into an issue tracker), plus it possible to edit the board at a later date.
Using the real-time collaboration version of draw.io (Google Drive only), each user can work in real-time with the others on the board. At the end of the process, each user can pick a pin color and use those pin to apply votes.