New jailbreak tweak dubbed as PerfectFit resizes outdated apps to support newer iPhone resolutions. When can it come in handy? As you may notice there are some apps in the App Store which the developer has forgotten to update the interface for the latest iPhone resolutions. This means they’re still designed to work on older iPhone like iPhone 4s or earlier, and this leaves unsightly black bars at the top and bottom of the app. So if you install such app it won't look nice on your new iPhone 6s or iPhone 7.
PerfectFit is the jailbreak tweak by Tony Kraft that fixes this problem by forcing these apps to run at a much more native-feeling resolution so they look better too.
Look at the example image below. As you can see PerfectFit takes an app with a dated resolution originally designed for the iPhone 4s (or earlier) and actually re-sizes it very nicely for iPhone 6 Plus.
You can download PerfectFit for free of charge from Cydia. The tweak works great on all jailbroken iOS 10 devices. Once installed PerfectFit will add dedicated preferences pane to the Settings app. Here you can select the apps you want to toggle the tweak’s effects for:
All apps are disabled by default, just toggle on those you need to be updated. You will notice that the tweak doesn’t just ‘stretch’ the app to fit, but it actually does things the right way, providing the proper zoom setting and the clearer resolution as well.
There are bulk of apps in the App Store that you would actually need PerfectFit for these days as they've been updated. So if you have found some you can use the tweak to resize outdated apps to support newer iPhone resolutions and make them look great on your device.