I'll attest to Dorothy's and add just a bit more. An application reflects who applied for credit, the program applied for, who took the application, and all financial details in-between.
For residential real estate loans, the app is required by secondary marketing as an attestation that all is complete. There are 2 applications actually required - initial application - what was requested by the borrower, from whom, & signed by borrower and loan officer. The final application - what was verified and validated during processing. The customer signs that one too.
Above the signature block on a standard application are multiple reps and warranties that the borrower signs (but rarely if ever reads). These include the ability to reverify anything on the application, accuracy of the information, etc. Like Dorothy said, it's a great safeguard.
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Integrity. With it, nothing else matters. Without it, nothing else matters.