It would be hard to imagine Revit without layers. Unlike the layers in AutoCAD, the layers in Revit are not only used to display the individual storeys - this is actually more of an additional function. First and foremost, levels are invisible references to which walls, furniture and other objects are linked. This link also offers a decisive advantage: if the storey height changes, all elements move with it. Sounds like a dream! But unfortunately you often come up against the limits of this dream - for all their flexibility, the levels are always horizontal.
This is where the reference planes come into play - these can be placed anywhere in the room using a view. Once the reference plane has been placed, walls, for example, can be linked to it.