Question

Why should "for deposit only" be written on a check along with the bank account number when it is endorsed?

Answer 1

Because if you write “for deposit only” on the back of a check made out to you and then sign your name, then the check can only be deposited in your own account. This is called a “restrictive endorsement,” and it should prevent you or any other person from cashing the check.

Answer 2

so that nothing else is done with when the owner isn't holding it