I am a 3d modeler (I use Blender since 2.67). But I've seed an ad of a 3d scanner (I don't even remember which one it was) so I started to research them. I was mostly interested in reviews, but when I google it, almost all what I've find is "top 10 3d scanners in blabla year" or "top 10 cheap 3d scanners" or top 10 whatever, that doesn't provides much about user experience and actually looks kinda advertising. The only real reviews I was able to find was this cool guy 3d Scan Expert and he really seems to be an expert and a guy (or guys) who simply call themselves 3dscannersreviews.com, and they have, well, decent reviews. Also what I've found is that almost all manufacturers says, that 3d scanners are the easiest and fastest way to get a good 3d model. But, when I search for examples of 3d scans, most of the models had very messy mesh, detailed but messy, sometimes fused to the ground or rotating table and very simple textures, just color map, that contains all reflections, shadows, etc.
Well, to be usable they need retopology, and complete redo of textures. This is not "the fastest way to get a 3d model" you would spend same time for retopology as you would spend to model a proper mesh from start.
For 3d printing? yes, I think they can be used for 3d printing, but how often do you need to print a copy of something? If you need to replace a broken part, well, I see that scans has topology with lot's of small imperfections, so a simple 3d model from any CAD of just blender has much cleaner shape.
So what is a advantage of 3d scanner after all? The only Idea that came up to me is a scan of a human face, if you need a digital copy of this exact face, then yes, with all this messy mesh it still would be faster.