As an iOS device owner, it can be tempting to "free" your iOS devices from Apple's seemingly stringent limitations. I have never jailbroken my iPad or iPhone, but two of my personal pet peeves include the inability to download files greater than 50mb over 3G, or to delete Passbook and Newsstand from the home screen. I can resolve both of these issues through jailbreaking, yet I remain hesitant.
My hesitancy has nothing to do with a belief that iOS is a thing of perfection beyond reproach. Hacks that augment the operating system's multitasking capabilities also consume additional memory and processing power — both of which are scarce on even the mightiest iDevices. The end result is instability, and an unpleasant experience that one should attribute to a specific hack, not to iOS.
Security is another concern. Oftentimes upgrading to the latest operating system removes jailbreaks and their associated modifications. Because of that, many jailbroken users deliberately run out of date. They're left with potentially exploitable versions of iOS, anticipating an updated jailbreak that may not arrive for months. Aside from security concerns, the newest apps may not even support their antiquated iOS build.
The tech savvy have a tendency to recommend jailbreaking to their friends, sometimes to gain additional features or themes, and at other times to simply load software obtained through arguably unscrupulous channels. These iOS newcomers may not realize that jailbreaking makes their online experience unsafe, or even that their freely obtained apps could contain malware.
Lastly, although some individuals may believe they're a Jonathan Ive in the making because they have obtained a copy of Photoshop, the reality is much less alluring. Frankly (and with an unapologetic lack of objectivity) I believe most homebrew iOS themes are ugly, and think there is a reason Apple has never hired a 13-year-old to design its user interfaces. The image below is a prime example of a well-intentioned yet undeniably unattractive iPhone theme.
That said, perhaps the risks of jailbreaking do not outweigh the benefits for everyone. Freeing one's device will not necessarily result in a superior user experience though, and can in fact be much worse with regards to aesthetics, stability, and your device's overall security.