The basic idea of extrusions is to get a “light-weight” object (regarding data-size) and as far is i understood also meshing is one of the bigger parts of the data in a standard .3dm file.
(if you “save small”, rhino will not save meshes, and recalculate them on opening).
So this concept only makes sense if the mesh-command respects it.
So extrusions will help you, if you model a house or half a city for example, with a lot of wall s etc … all extrusions … so you have a smaller file size, and less work for your graphic card.
Extrusions as object-type is not a modelling feature, it is a data-management-optimization
as al extrusions can be converted to Surfaces / Polysurfaces
_useExtrusions as a general setting
_convertExtrusions to help you for special cases where you need other meshing.
for all other operations e.g. Boolean stuff, trimming, … rhino will handle everything in the background for you.
hope that helps, best, -Tom