Thats why one is called Painter and the other Designer.
With Designer you can create Materials, with Painter you can paint these materials.
Designer is node based, very procedural and flexible, but more for technical artists.
You can mix bitmaps, vector graphics and procedural stuff. It basicly creates shader networks, but the good thing is you can import them to Maya, Cinema, Unity, Unreal etc...
The procedural parameters stay exposed and you can always generate countless variations and changes in quasi realtime.
Painter is great, but Designer is the real game changer.