When I owned an iPod touch, the advantage of jailbreaking was to give your device certain features that the OS just didn't support. (Hell, I remember early days when iOS didn't even have a concept of wallpaper, the background was just black.)

iOS has come a long way since those days so a lot of the most common use cases of the past are no longer necessary. But the principle is the same - the hardware is a general-purpose computer but the software is locked down unnecessarily in many ways. Jailbreaking lets you do things that are outside of Apple's box.

A much-needed advantage is also keeping old devices useful. Every Apple phone slowly outlives its supported software to the point where the official AppStore has almost nothing in it. Today, it's extremely difficult to find 3P apps that work with my current iPhone 7, which is not that old, because the ecosystem cuts off old phones very quickly.

I agree, and, if you have a developer certificate from Apple, the list of wants I have is ... not that long? zero? I'd love to be pitched on it. In practice, I wanted freedom, but didn't really want to do anything with it.