Yea, Member Builds are to document the process of how your truck got from point A to point B. It also goes into great detail.
Member Garages are to show off your truck as is. It's one location where someone can get all the details about your truck. So... if someone looks at a picture and thinks... I wonder what kind of tires he has. He can cruise over to your garage and find the info very quickly.
Make sense?