Your question sounds like something a teacher would ask for an assignment ;)
I like to think of the WBLOCK command as AutoCAD's way of giving your drawing an enema. I know, gross analogy but I think you get the point.
It cleans out all the little bitty left overs that the PURGE command may not have gotten rid of.
I guess the same can be said about the EXPORT command as well.
Now, I don't know how much of a difference it makes if you WBLOCK everything (i.e. *) but if you block out SELECTED entities, AutoCAD only brings those entities into the new file.
Where as performing a [*] at the command prompt does not totally clean it out.
I do use PURGE a lot though, but my drawings don't get big enough where I need make the file really small.
I PURGE mostly unused layers, DIM styles, text styles, etc.
But if I get a really large file and I only need to work with certain areas of the drawing, I will WBLOCK it to a new drawing or EXPORT the info.
