From my experience, especially with psilocybin (shrooms), the main benefit is not hallocinogenic at all (at a ~2g or so dose) but that it has the effect of basically forcing you to confront all the emotional pain that you bury and ignore. I always end up laugh-crying and experiencing revelations about myself, my relationship etc that I simply don't have otherwise. I can see how effective it can be when taken while in therapy because you basically force yourself to open up. It's a truth serum, of sorts.

I have not tried DMT but my understanding of ayahuasca (active ingredient is DMT) retreats in places like Peru is that it's like "10 years of therapy in a week."