Medication (and mother substances) can affect your ability to have dreams, and what they are about too. Depends a lot on the type of medication and your specific case (not everyone reacts the same to each medication), so YMMV. I’ve been in treatment for depression for over 20 years with different medications and therapy styles and definitely I saw significant differences.

Maybe not evolutionary advantage, but vestigial origin. Maybe a feature that is in the middle of development / disappearing.