Well, it depends on which version of "GPM" and whose version of such. Hubbard released two versions, and each of which were processed differently at different times

And, of course, others have released their versions of "GPMs".
So this is really a generality. And honestly it is not a subject I'd get into "debating."
It is true though, that folks will feel some change/relief/gain/whatever from addressing the notion of GPMs; and it is equally true that some folks will get very screwed up by addressing some versions of it.
My view of it is that it is an "almost" right item . . . "GPMs," no matter whose versions or which version of them, do contain some concepts that are common to we spiritual Beings.
And addressing such concepts will give a person some insights.
The error in the notion of "GPMs" is that "this is the issue that is dominating you, controlling you, and containing you . . . and when run you'll be free!"
That is a huge error and a mis-director away from the actual truth of the scene to be handled. But then, maybe that is why so many, as Hubbard did, dive off into this "solution to 'your' case."
The actual scene to be handled if one is to "make it all the way out," is rather horrifically charged. Which is why it gets avoided like hell with diversions like "GPMs."
The bottom line that has to be addressed and resolved if one is to recover the real you and its attendant or composite truths is the following.
One needs to address the wholeness of your true presence of Being, virtues and powers and the misuse of such. That is, the violations committed by their use by you and others, both on self and on others.
And part of the address to this or these basic truths is the address to the solutions one put in place to handle those violations and misuse of power.
Fiddling with "GPMs" is rather like rearranging the furniture in a prison cell and feeling freer and better because of it.
Rog