There could be a lot of reasons why someone would need the bundle ID of the apps installed on their device. Like one is the tweak IconBundles. What it does is let you theme the main icons with the BundleIDs. Another would be if your making a tweak. You need to know the BundleID to filter the app in your tweak. 

So for whatever reason you need the BundleID of any app you have installed the app BundleIDs can supply that for you with on click. You just go into the app BundleIDs and its setup a lot like WinterBoard. You just find the app you are looking for and click on it. It will show a popup of the BundleID and let you copy it to your clipboard. 

So if you need a BundleID for any reason get to Cydia and get BundleIDs for free!