Using a bathroom corner medicine cabinet is a good way to save space, particularly if the room is small. If the bathroom in question is just a half-bath, such as is often used for guest facilities near a party room, then the situation is even more critical.
Unless you are a contractor, you probably are not aware of what your local plumbing code has to say about the placement of bathroom facilities. A toilet must have at least 30″ of space to sit in, and a sink needs 20″. This means if you are considering installing both these fixtures on the same wall, you would need over 4 feet of wall space.
By putting either the toilet or the sink in the corner, it will need less space on that wall. So if the wall is long enough, you will be able to put in a somewhat bigger sink or vanity. Manufacturers of bathroom facilities know of this, so many of them make corner fixtures.
One difficulty with putting the sink in a corner is that bathroom corner medicine cabinets are not able to be recessed into the wall, so they will stick out into the usable space over the sink. If this is a problem, then you could use a recessed cabinet on one wall of the corner, and put a mirror on the other wall.
When it's time to choose a corner medicine cabinet, you will be somewhat limited in your selection, since demand is not as high for this feature. Even so, the other features you may be looking for are available: wood or metal doors, mirrored or unmirrored, glass or metal shelves, towel racks.
Prices range from about $150 for a simple NuTone metal cabinet with mirror to over $1300 for the ultra-fancy Robern Deep Corner cabinet. This even has a swing-out magnifying mirror in addition to the large beveled mirror in the door. And it has side-lighting, which gives your face a more flattering look.
So for a small bathroom, a corner cabinet may be the best way to save that valuable wall space. For more ideas on choosing bathroom medicine cabinets, see the author's website below.