I have multiple playlists where one is maybe a subset of another list:
Currently when you want to add a track to both playlists, you need to add the track TWICE (can consume much time on the mobile phone, if you do that often).
It would be cool, if you could click on "Add To..." and then on the next screen you could select as many playlists as you want. The track would be added to all of the selected ones.
Update: This idea has been suggested again here:
This idea has been submitted more than 1 year ago but unfortunately hasn't gained enough kudos during that time (10 kudos/year). In order to keep an overview of the active ideas in this forum, this idea will be closed for now. Note that this does not mean the idea has been declined by Spotify.
Please feel free to re-post this idea if you still feel you want this implemented. With a little change in presentation, maybe this time it will gain the necessary support from the community.