What is the purpose of this?
Unlike most other instrumentalists and singers, those who play the piano often do it without making music with other people. A drawback to that is that it can be a solitary activity and it is easy to become unaware of bad habits, such as getting slower or quicker.
There is great educational value to playing with others, not least in the aural skills that it teaches you and the increased awareness you get about your own playing.
Not only this, but it's great fun!