Benefits of using 3D Solids
There are certain benefits when you use 3D solids. From 3D solids you can read mass, volume, centroid, moments of inertia, products of inertia with the MASSPROP command. This information is not possible to get with a box build with surfaces. The exception here are regions. From these you can read area, centroid, moments of inertia and product of inertia. And it's easy to edit a solid with grips. Moreover, you can easily create holes, fillets and chamfers on a 3D solid. Additionally, you can use boolean operations on solids, like intersect, subtract and union. My advice: Always use 3D solids or regions, when it's possible in AutoCAD. In architectural design, use region for the floor. Because it's easier to get the area with the Massprop command.