Most times, a flat, plain slab of mirror running horizontally in a bathroom is the product of a builder’s knee jerk reaction to how bathroom design is "supposed" to look and function.

After all, mirror expands a space and people like to look at themselves. Right?

Mirrors aren’t all that costly, but because a builder typically doesn’t want to spend money where it doesn’t count they most likely won’t take the mirror over 7’ high because most people aren’t that tall. Right?

Of course! I've seen it and you’ve seen it. In fact, you probably have one in a bathroom right now, with a little vanity light above it.

Here I used a horizontal slab mirror to expand the width of the room. I extended the counter over the toilet with the mirror and took the mirror with it to create the appearance of a larger vanity.

Personally, I'm am a big fan of tall, narrow mirrors.

I think they make a bathroom grand, luxurious, and heighten / enlarge a space immensely.

However, there are instances when a horizontal slab of mirror -- when done purposefully, keeping the overall design in mind -- is the absolute best solution. Instances such as...

When a horizontal banding is defining the design of the room.
When that horizontal line does not need to be broken.
When a horizontal element -- like recessed lighting or a long countertop or shelf -- works with that mirror shape and size to create design-intent.

That’s when a horizontal slab mirror is appropriate. That's when it becomes the best thing for the job.

Right? ;-)