That is actually VERY interesting. Thanks for posting that. It looks like I've treated one of my issues using this approach, though I'd never heard of it before.
Going to post this not to debate religion, but to show this can be a VERY useful therapeutic tool.
Classic PTSD nightmares plagued me for years, I'd be waking up terrified several times a week, at times. They always revolved around past trauma, things that happened literally years in the past. I spent a long time wondering how exactly that works, why I was haunted by this stuff years after - then stumbled on the idea of subconscious desensitization. That something in my mind was generating nightmares, to make it easier to deal with the subject matter when it happened again during waking hours.
That idea meshes with the IFS idea of the various subpersonalities having positive intent, even if what they do is counterproductive. Seeing them as something separate from the self matches the whole concept...
But it's important to note, it is only a useful fiction. The language of psychology isn't quite up to the task, so an analogy is necessary. They are not demons, not dead people and not channeled spirits. Not alternate personalities. Instead they are complex thought processes that have become so automatic they've faded from awareness and sunk into the subcionscious. Just parts of the mind, which is a very complex thing, and they can also be complex.
Anyway, given the above, I talked to myself about it for three-four weeks. Not literally. Sometimes it'd be a few minutes of a day of just thinking about the idea. Sometimes meditation, sometimes stoned and usually sober. I told myself, or some part of myself anyway, "that was good, that was useful, but you may stop now." Eventually I woke up from one and instead of fear felt only a mild annoyance, turned over and went back to sleep.
Before, I suffered these nightmares often enough that I became afraid to sleep. Last year I noted them twice. This year, none so far.