Above the Mirror
While sconces can be fixed in several locations, many fixtures are appropriate only above the mirror. Many bathrooms are already pre-wired to accept a vanity fixture directly above or on the mirror. Many people prefer this location because of the flexibility it offers in terms of vanity light width. A vanity light above the mirror also provides a great amount of lighting because of the amount of bulbs they have.
Sconces beside a mirror

Sconce above a mirror