What is the use of plane mirrors?
Plane Mirrors are used when you want to directly reflect an image without any distortions. These mirrors are used almost everywhere in daily life (Bathroom, Rear-view, etc)
Plane Mirrors reflect light back at the same angle as the angle of incidence. See the Picture below for a visual representation of this:
Notice how (with my sloppy paint skills) the two angles
This is different from other mirror types that will distort an image depending on the shape of the underlying reflective surface.
Any mirror that appears to zoom in or out (make-up mirrors for example) are NOT plane mirrors.