Users who don’t want redundant dependencies will probably prefer AUR packages. It can also be nice to manage all the packages with just the helper app. I try to install the binaries of apps from the AUR if they’re available to avoid the long build times.
While the obesity part is kind of a digression, I think they were pretty clear: protein powder is a waste if you have a typical American diet and are not exercising, which is apparently most Americans. While protein powder on its own isn’t snake oil, it effectively is for most people.