A Terms and Conditions agreement acts as a contract between you and your users.
There are five reasons why a Terms and Conditions is necessary:
Prevent abuse.
This is especially necessary if your app or website allows for interaction between users.
Users will not want to use your website/service or service if defamation, spamming or other abusive behavior is uncontrolled.
Without a Terms & Conditions, you lack the authority to suspend or ban users who display problematic tendencies.