If you paid a bill and wrote your check as 01/02/20, the receiver could alter the check to read 01/02/2021.

If they didn't cash the check then your bill would not as having been paid and they could scam you into late
fees or non-payment on a debt that was due by the end of January 2020.

Chances are that you would catch the error when your check didn't clear but some people never look as their check statements and wouldn't know.