Jailbreaking an iPhone allows users to gain root access and full control over the device. It breaks through hardware restrictions to let users install unauthorized apps, modify settings, and access restricted files. However, jailbreaking voids the device warranty and can potentially make the iPhone less secure or cause apps to malfunction. The document discusses the benefits of jailbreaking, such as customization and access to unauthorized app stores, but warns that it should be done carefully to avoid data loss or security issues. Unlocking refers to removing carrier restrictions on a phone to allow use on different networks, which is a separate process from jailbreaking.