Someone will trip on the mistake and report the bug and you fix it.

You dont get a compile error if the documentation is wrong. Chances are you wont notice.

And even if it eventually is fixed it is not obvious that the reason for the bug was that the documentation was wrong in one particular place.

And by then you have several people on the team who have thought the wrong way is the right way for months, never mind your support team probably giving end users bad information.

It's messy.