For me...the groups/marketplace is similar to what ebay did 15 years ago for collectors. Lowered prices and dramatically increased supply. There was a specific cruise control set up I had literally been searching for, for over a decade, never could get a lead or even find any that weren’t for sale. In the last 3 years, I’ve found 6, and bought them all. I probably buy $1-2k in parts/month that way.
Another benefit I enjoy are the discounts and free swag I get from the businesses I let advertise in my groups.