Kyle Matthews på ModMyi.com i en lång text om varför jailbreak har betydelse och vad det inte är:
At it's core, jailbreaking is not an app, it's not Cydia, it's one simple thing - having unrestricted write access to your device. In more technical terms, it's having root access. In the Android scene, it's actually called rooting your device.
So what's the big deal you ask? Maybe you're not a hacker, or even a "hobbyist" or "enthusiast" - that's fine. Maybe you don't care about having any access at all to your device - it does everything you need already. You don't want to jailbreak, and you never will. That's fine, and for many, true. My iPhone 4 isn't jailbroken yet, and it's been handling itself just fine - of course there's tons of jailbreak apps I miss (Notifier, Tlert, MyWi, WinterBoard, iFile, and OpenSSH/SSL being some of the biggest). But if I /want/ to modify my device, which I have purchased and own outright, for completely legal activities, enhancing the original purpose of the device (a "smartphone") - it should be legal. Whether I do so or not should remain wholly my choice.
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Many people seem to associate "jailbreaking" with "iPhone piracy." This is a flawed view. Piracy IS illegal, has been clearly defined as such legally for years, and is not at all synonymous with jailbreaking. Take ModMyi.com as a case study - we have over 675,000 members, the vast majority of whom have jailbroken one or more iDevices, and we strictly forbid any talk, linking, or mention of pirated apps. I personally have had a jailbroken iPhone longer than nearly anyone here (ModMyi actually created the first ever iPhone "theme"), and I have never pirated an iPhone app. It has always been our standpoint piracy is 100% illegal, and is rude on top of that. Devs spend days and weeks building $2 and $5 apps - if you want them enough to install them, you should pay for them.