Client first empty divs for spacing?

In regards to client first framework…

Why use empty diva for spacing over just using margins on a section or container? Forgive my ignorance but when I dabbled in xhtml and table based layouts we used empty diva and stuff for spacing and it was considered bad practice. Is it bad practice to use these spacing divs to create space vs margins css on the sections themselves?

I have followed a couple of the university course and they just use margin and padding and when I decided to dabble in frameworks I just want to make sure these are good practices.