Mirrors are useful for more than checking your hair or straightening your tie. With them, you can collect information. Does your library have a barcode scanner? You're making use of mirrors to gather information about the items you're scanning. Clothing stores are starting to experiment with combining RFID tags and mirrors to make for a method of trying on items without ever taking them off their hangers.
But those are small time things. You want to see where mirrors are used to collect information, you look at astronomy. For instance, you look at one of the mirrors used in only one of the units in the European Space Organization's Very Large Telescope array. Those are serious mirrors.