There are many reasons to hide yourself online. IP addresses can be used to discern your physical location, and can sometimes do so with remarkable accuracy. These addresses also act like personal identifiers, a little like a phone number, letting advertisers and adversaries track you online. They can also be used to launch targeted attacks against you.
You may even be hiding from a watchful or oppressive government. Journalists are especially likely to hide their IP addresses when they’re reporting in dangerous areas or on sensitive subjects. Of course, I’m not encouraging anyone to break local laws, but I do want people to know how to keep themselves safe, should the need arise.