According to the AutoCAD help file, “Reconciling new layers is the process of manually reviewing new layers so that you can avoid potential errors before plotting your drawing or when restoring a layer state.”
I can see how this would be a really great tool but I haven’t fully adopted it because I would need to setup the template to contain all our standard layers (most of our layers are created on the fly through macros) and thus I would be getting notifications constantly as new layers are created. But we might consider setting up our template for this in the future.
Here is how layer reconciliation works: Setting LAYEREVAL to 0 turns the layer reconciliation feature off. Set it to 1 and it will detect new xref layers. Set it to 2 and it will detect new layers added in the drawing and xrefs.
When you open a drawing that contains unreconciled layers, you will see this (AutoCAD 2008):
When you plot a drawing that contains unreconciled layers, you will see this:
I think layer reconciliation is worth taking a look at, especially for companies that want tighter control over layers that are being used.