The advantages of using multi-factor authentication (MFA) in online systems include enhanced security and reduced risk of unauthorized access. MFA requires users to provide two or more verification factors, such as something they know (password), something they have (smartphone), or something they are (biometric). This layered approach makes it significantly harder for attackers to gain access, even if they steal a password. By implementing MFA, organizations can safeguard sensitive information and account integrity, thus protecting against data breaches and identity theft.