While the Dancercard will still be used for Just Dance 2017, it is a player profile/account used in-game: it's the Global Account, on top of the Dancercard, that will keep your information and progress.
The Global Account is cross-platform, and it doesn't matter if you play, for example, on a PS4 while your friends play on Wii U, or if you are playing on Xbox One while your friends do so on a PS4.
This means that you can be playing at a friend’s house, using your own Dancer Card during this session. As long as you are identified by your Global Account, you can while using your smartphone save the high scores to your account.
However, the Global Account is optional. You can still play Just Dance 2017 but without it, the only thing that will be saved cross platform is your profile info and your flag, not your score or progress
If you would like to know more about other features of Just Dance 2017, check out our related FAQ.