Has happened in the past history of earth where quite massive 'rocks' hit but even a small one can be damaging to a small area like the one that exploded over Russia just a few years ago.

That is why there is an organized effort to spot them before they get here then maybe there will be time to do something about nudging them away from a damaging course.

Apparently the one that just missed although it was not really big was also dark so it did not reflect light to make it easier to see.

There is a list of comets and asteroids that are potential threats to the earth in the next 100 years some are as big as .5 km across but even the .1km rocks would make quite an impression on earth and there are a couple with potential strike capability just in the next decade.

Trust those watching them have a good plan too.

https://cneos.jpl.nasa.gov/sentry/