Jason,
Frankly... the Practice Guide is nothing more than a "pared down" version of PMBOK 6.
After releasing PMBOK 7, PMI realized that it's impossible to lead a project using "all the fluff" that is discussed in this new version. Instead of a list of principles, project managers want a more "prescriptive" approach that tells you what to do first, second, third, and so on. So they took PMBOK 6, which is somewhat prescriptive, and reduced it to its core process descriptions. Then they published it as the process guide.
That much said... reading the process guide will give you a good understanding of the PMI framework and its processes. So it definitely won't hurt in your exam prep.