One can work without scene management tools, but I find it makes the workflow significantly faster and more organized. I’d put it on par with having a layer editor. Anything that can speed up productivity is a welcome addition.
Edit: Just to beat a dead horse, here are some videos of The Explorer window in XSI and the Outliner window in Maya:
(XSI) https://www.youtube.com/watch?v=NQbg31yV338
(Maya) https://www.youtube.com/watch?v=zPMJUQqeXks
(Alias - Object Lister) https://www.youtube.com/watch?v=GyJXBxLF2PQ (0:18 to 1:00)
I think the interface would translate very well to Rhino. It’s a parallel and similar idea to the Layer Editor but with more granularity and functionality. Any additional functionality that works on the object and sub-object level (as opposed to strictly groups/ sets/ classes) of would be a welcome addition.
An obvious example would be each layer in the layer editor having a collapsible list of the objects it contains. Each object in the layer could have the same individual controls as the layer (but subordinate to the layer itself).