Plot-paris
I personaly find this sort of layer structure too complex. I guess if you are sharing information and working on medium to large schemes it will be important to structure the information. I found that, when I worked in an office trying to impliment this type of formal structure, getting people to adhere to it was very difficult - so the system tended to fall apart at the seams. (Do some CAD systems force you to organise in this way?)
I took a lead from one of the SU workshop lectures and now use groups to the same end, keeping it simple - just, 'Ground floor', 'first floor', roof, etc.
I find that manipulating information using groups and the 'outliner' facility in SU, allows sufficient control, and is something that was not available in CAD.
However, I think the main thing is to find a system that works for you and there are many ways to organise the model information.
David