If your application depends on Commons Codec library (version 1.4 and above), and you are not aware that Android framework already includes this library, then there's a chance that your application will crash with a runtime exception.
Why does the Android framework includes the Commons Codec library?
Android framework shipped with HttpClient (version 4.0 pre-BETA, an ancient 2008 release). HttpClient depends on Commons Codec. Therefore, AOSP had to include Commons Codec as well.
OK, so can I use framework's Commons Codec library in my application?
Unfortunately no. This API is hidden and not exposed in Android SDK for application developers. You can invoke the library's classes using reflection of course, but by doing so you take the risk of relying on undocumented APIs, which is not recommended at all.