Applying for a loan with a co-signer who has excellent credit will greatly increase your likelihood of gaining loan approval. The role of a co-signer serves as an extra layer of protection for the lender. The lender gains security because the co-signer is on the hook for payments if the primary borrower can't make them. Because of this, having a co-signer can earn you a decent rate and term, even if you don't have the best credit.