Payday loans structurally require you to be banked.

The offering is "I will advance you $400 in cash today for a $415 check dated in a week. You can come back and buy your check back for $415. If you do not, I will deposit it." The security here _is the check drawn on your checking account_; without that the payday loan has markedly higher collection costs and markedly lower probability of collection.

Also, they use the fact of writing a check to (in some jurisdictions) gain legal leverage that they would not otherwise have access to, because making someone a promise to pay and failing to follow through with it is generally under the notice of criminal law, but (in some jurisdictions) writing a check which one knows to be unbacked by funds is a criminal offense.