Sometimes a mirror will draw you in, like a moth to a flame. It may enhance an existing focal point, like a fireplace...or, it may be so stunningly beautiful, it "becomes" the focal point.
A mirror will often increase the bright, airy feeling of a room, reflecting the available light right back out into the space.
Mirrors are sometimes used to make a room feel more open and spacious. In addition to making a room feel more open, they may even serve a "safety" aspect, providing feedback that an exercise is being performed correctly.
A mirror could fool you, pretending to be only a mirror, when in reality it's a door to a secret hiding place.
Often, they serve a utilitarian pupose, assisting us with getting dressed, styling our hair or applying make-up.
They will even obligingly stand in place, when there aren't quite enough photos to really fill a space.
A mirror can give a room a sense of history with years of wisdom etched all around its beautiful face.
And sometimes, they reflect a view that will simply take your breath away. ~SIGH~
A mirror might add drama, beautifully filling an awkward area that would otherwise go lacking.
It might even remind you to lighten up and not take life too seriously, with its fun, whimsical design.