After having installed Combined Community Codec Pack on your fresh Windows System, you may stumple upon some real video files which don't play back (f.ex. Real Video 4.0 format isn't supported by ffdshow from that codec pack).
But there's still no reason to install the oficial Real Video package, which clutters your system with unnecessary stuff (that codec really sucks, go for x264 instead).
With Real Alternative you can play Real Media files without RealPlayer.
The pack can be used with any DirectShow-enabled media player, such as Media Player Classic, which is included as part of the package.
As you already will have installed the CCCP, you can just install the Lite version, which doesn't include Media Player Classic.