These machines are very useful. Ironically, in spite of the name, the most useful functions are not in computing things at all. Mostly they are useful in storing information, and accurately retrieving it - even from long distances through networks like the Internet.
Even a small, modern computer can accurately store more information than a human can, and can share that information with more people than a human could. Computers can understand data and information, but not knowledge or wisdom.
See