Difference between stacking and extruding meshes? What would be the difference of stacking objects into each other and extruding by starting with one single primitive. How does it influence performance and what are the advantages and disadvantages using either of them?
For reference. Between this

and this
I would recommend using one mesh. You can easily get the mesh you want in this instance by selecting the desired face, pressing E to extrude and then S to scale. Now press E to extrude again, and you have the desired mesh, created in three simple commands.



This method works in many other instances, even on N-Gon or Tri faces. This is a good general modelling technique to know for any modelling project.