I won't pretend to know much about WordPress, but "framework" in various parts of web design means a bunch of ready-made code that provides a starting point—rather than you having to do everything from scratch. In other words, a lot of the hard stuff is done for you already.
In terms of building WP themes, it's probably better to learn how to do this from scratch so that you better understand how themes are built and how they work. Still, a framework will no doubt save a lot of time.
A theme framework probably does come ready to use, but its real purpose is to provide a starting point to which you make modifications. It's unlikely that any theme you pick would be ready to use, as you've at least got to change the title and default text.
Anyhow, I'll move this thread to the CMS forum and let experienced practitioners give a more knowledgeable reply.