I do it for integration with Google Voice (with Phone GV and SMS GV) so that I can place calls from the built in dialer and send free texts through Messages.

The other thing I use frequently is NCSettings, which is much like SBSettings, but well integrated into notification center. It has a couple of pages you can swipe through, and gives immediate access to toggles for wifi, data, volume, brightness, VPN, location services, and more. http://modmyi.com/info/ncsettings.php

I also use Chrome on my phone, mostly because I use it on my desktop and laptop and like to have access to open tabs from my computers. It's doable without jailbreaking, but being able to set it as the default browser makes it a lot better.

If you work in mobile security, you essentially have to jailbreak the devices you use for testing. Things like being able to edit /etc/hosts are critical, as is being able to decrypt applications for analysis.

For most people it's about customizing iOS: adding extra features to the interface, disabling features you don't like, personalizing how it looks - generally finding ways to improve it so that it works better for you. Instead of just looking at interesting concept designs for new iOS features, you can install them. Here's a long thread from the jailbreaking subreddit where a bunch of people discussed the first packages they planned to install after jailbreaking: http://www.reddit.com/r/jailbreak/comments/17gm4g/since_this... - I think it provides a decent cross-section of some benefits that people get excited about.

Also, if people are interested in technical details about what the jailbreak actually does, this old HN thread with comments from saurik is very informative: http://news.ycombinator.com/item?id=4127801

Generally it is getting less useful but there are till a few tweaks i couldn't live without: zephyr - task switching via a 2 finger swipe. A great way to switch back and forth between 2 apps Swipeshiftcaret - move the cursor around by swiping rather than having to hold and then position it, which I always find fiddly. Great to make quick corrections. AndroidlockXT - unlock my phone via a swipe pattern rather than a number code. Looks much cooler and is quicker I feel. Sbsettings/ncsettings - easier access to things like wifi and Airplane mode which I use more often than you think

There some other ones like 5 icon dock and double decker switcher which are cool but not really essential. And zeppelin to change my carrier name to any logo I like.

The big one for those of us with an AT&T unlimited data plan is tethering. They had to grandfather our plans in because they sold them to us as unlimited, but they will not offer tethering as they are trying to force all users off of those plans and on to the 5GB plan.

Do those apps actually still work on AT&T? I thought AT&T detected their operation and blocked them.

They still do work, PdaNet has an option to hide the tethering from AT&T. http://junefabrics.com/iphone/index.php

They certainly did on my iPhone 4 (as recently as 6 months ago). I haven't tried it on my iPhone 5, though, because I haven't jailbroken it yet. I guess I'll find out soon enough.

I believe it is becoming less and less useful. To begin with, it was the only way to get any third party apps on iOS devices. Later it became the only way to have custom wallpapers, multitasking, better notifications etc. Obviously all these things have now been added officially, and in most cases the official implementation is more user friendly and more integrated.

There is still increased ability for theming with jailbreaking, and some unapproved apps such as emulators etc. as well as a few general tweaks such as allowing extra apps in the dock or allowing the home screen to be rotated on iPhone, but the benefits are slowly decreasing as iOS gets improved. But there is still benefit to it for some.

It's the same case with rooting Android devices; at a time it was almost essential to address the shortcomings of the OS. Now, it is barely even required for most users, due to the improvements of the OS. (stuff like taking screenshots, making backups of app data, tethering etc. used to require root on Android; now it's all baked right into the OS)

I'd say it's noteworthy though that these features may never have made it to their respective official OSes had they not been so popular with jailbreak/root users, so it's an important part of the OS improvement process in my opinion.

I still use it for SBSettings, which allows me to turn bluetooth, wifi, etc. on by swiping the top of the screen.

And I use it for tethering or setting up a wifi hotspot from my phone (MyWi).

Plus a bunch of other things :).

Consider NCSettings. It's slicker than SBSettings and doesn't require activator if you're one of the many who have a thing against activator. It builds itself into the notification centre rather than replacing it with its own.

Most people have already replied why but I just want to touch on the point of updating the OS: I just do not do it. What's the point anyway?

I only upgrade when too many apps stop working or when I brick my phone. I think I have upgraded my 3GS two times now.

I know some people use it to do a proper replacement of Apple Maps.