One of our "3D Printerns" (students who are spending 8 weeks in the department over summer working on 3D printing) was using this today. It reminded me that I really ought to tell the world about it. (like my blog is some kind of public service or whatnot.....)
Anyhoo, one of the problems with making 3D models is that sometimes you get bits of data in there that just don't make sense from a 3D point of view. Elements can intersect in odd ways or you might get tiny holes in meshes. These imperfections can cause all kinds of problems when you try to move from a model to a physical artifact.
Normally you need a person to go through and tidy the model it up, but Microsoft have a free, cloud based, service that will just accept your models and tidy them up for you. It's all free, and very useful. You can find it here.