When is it necessary to `enableUtf8Validation`?

In the v4.3.0 of the Node driver, the enableUtf8Validation option was added so that it can be disabled for a performance improvement, but I have no way of knowing whether it is okay to disable. In what circumstance could updating a string into the database lead to invalid UTF-8? Can I have any example code that would trigger the validator to throw an error, and/or a general explanation?