Carnitine, a rather clever small jailbreak tweak from developer ClausCartel on Twitter, allows you to keep WiFi shut off to save battery until your encounter an app that actually needs it. So, for example, when opening Safari Carnitine pops open a small dialog box with the option to turn WiFi on and connect to a network.
Such a tweak is obviously useful to those who value battery life, and need every radio shut off unless called upon. It’s also useful for those on limited data plans who want to keep their device in Airplane mode, but could use this tweak to automatically turn WiFi on when necessary.
As of this writing, the only downside is that the tweak doesn’t shut WiFi off after you’ve exited the application that needs an internet connection. Obviously a downside, as it requires a trip to the Settings app to remedy; hopefully this change can be made in a future update. Until then, those of you who are jailbroken can find Carnitine on Cydia in the BigBoss repo.