Glaze Medium, like the Matt Medium, Gloss Medium, and even the Thinner Medium, is an acrylic medium.  Think of them all as paint without the color, but all the polymers (the "glue").  They let us modify the behavior and look of the paint while preserving the integrity of the acrylic base.  We thin the color but not the acrylic structure itself.  Contrast that with using something like water where not only do you spread out and thin the color, but the acrylic itself such that fewer polymers "link up" resulting in a weak paint film.

The Glaze Medium in particular has the properties and effects you mention.  Its thinner than the matt/gloss medium, almost as thin as the thinner medium, and slows the curing (distinct from drying) waaaaay down.  I once used it by mistake instead of thinner medium when airbrushing.  Looked normal, appeared dry within a few minutes, but the next day I handled the piece and it came off on my finger.  I ran the piece under water and almost all of the airbrushed coat came off! So NOT good for doing opaque coats, but VERY useful for translucent effects and of course washes.  Also good for doing delicate mud/dirt/rust with pigments, but it doesn't "build up" as fast as when using the matt medium which is thicker.