Distorting reality, one pore at a time.
I refer to the 10x magnification side of a mirror "the scary side." Nowhere except in a magnifying mirror will you or anyone else see your skin that way. I've seen people obsess over pores, acne, lines, wrinkles, and freckles in a magnifying mirror, not realizing that their skin problems are just that- magnified 10 times bigger than reality.
Some people are obsessed with their pores. Staring at them magnified does not help the situation. Gentle chemical exfoliation, such as salicylic acid, or clay based masks are great for keeping pores clean and makes them appear smaller.
For people who pick at clogged pores and acne (I have been guilty too), these mirrors create a dangerous situation. Many pickers will torture their skin, squeezing every last pore until their skin is a damaged, inflamed mess, creating a situation for bacteria, dark spots, infections, and scars. Opening these lesions with the wrong methods will usually make whatever blemishes far worse and lengthen the healing process. Put down the hydrogen peroxide and thumbtack.
Staring at expression lines and other signs of aging can also be problematic, though to a lesser extent. A lot of people will point out their saggy skin by pulling their skin down, or their sagging eyes by tugging roughly at the fragile skin around the eye. Skin has 'memory', sort of like clay, and the more you pull on it the more saggy it will become. Obviously one or two tugs are not going to cause permanent damage, but if you have the tendency to do it, having a magnifying mirror in your bathroom and constantly staring at lines and wrinkles and poking and prodding will not help at all. Instead, use products with vitamin C, antioxidants, and peptides. Get a chemical peel from a professional.
Unless you're farsighted, or use a magnifying mirror to do your makeup or tweeze stray hairs (be careful not to over tweeze!), throw it out or give it to someone you don't like. It's just not worth it.