One legitimate use case is perhaps that in the olden days before in-app purchases, you could install an empty paid app that would than act as a token that would enable some functionality in another app. The second app would need some way of checking the presence of the first app.
you could achieve the same without in-app purchases or this API if you are in control of both apps. You could for example sign the app with the same key and gain privileges by that over your other apps if i recall correctly and if its still true.
