As the word manual suggests, this is a type of approval that requires a real person to take action, rather than letting everything to be done automatically. The number one reason why manual approval has an advantage over automatic is the security. The fact is that even today, in the 21st century, online fraudsters find it difficult to trick a real human. They might be able to find a way to go pass software check, but it wont be easy to cheat a professional. When it comes to affiliate marketing, manual approval is often a requirement set by the merchant. This is because they want to ensure that they wont get into a partnership with a legit affiliate.