Earlier quoted context omitted.
In a similar vein, a good friend of mine (+ all his family, about 10 in all) was kicked out of an AirBnB at the last minute because it had been double-booked on Booking.com at a higher price, and had just been rented via that site. I've come across a few such stories.
A family member of mine had something similar happen when using booking.com. She showed up at the hotel and they had sold her booked room to someone else. It was late and a bit of a nightmare to find another place to stay. Overbooking airplanes means someone might be stuck sitting in the terminal for hours. Overbooking.com means someone might be made to drive around late at night, tired, with nowhere to sleep.
It also might mean you miss getting somewhere in an emergency, like visiting a loved one before surgery. And it also might mean you miss things you couldn't miss, like a job interview.
One of the worst memories of my life started by missing a flight (and it wasn't my fault).