For the Ogg Media Framework
Within OggStream, codecs are recoded (encoded, decoded, or transcoded) from one format to another. For example, a Vorbis codec plugin could be used to convert a Vorbis I stream to a PCM stream. Ogg packets of these streams are imported and exported from OggStream, and several of these conversions can be used in sequence (plugin chaining) to attain a desired output from any supported input within that media type.
Some codec plugins will only support one or two raw codecs, providing translations between different formatting options as needed, such that (ie) if an Ogg FLAC file contains 64-bit float data, and the media player attempting to play this data only supports 16-bit signed int data, a second plugin could provide the conversion from 64-bit float to 16-bit signed int.
Having these uncompressed codecs is, thus, essential for implementing the new Ogg media framework as it depends on interchange codecs which all applications desiring to work with a certain media type can reasonably support.
For Low-CPU Storage
While losslessly compressed Ogg codecs are available for both audio and video, some applications (ie, live recording, editing, etc) find the higher CPU requirements for processing these formats less desireable than the need for additional storage capacity. Many of these applications require syncing information not provided sufficiently by RIFF (.wav/.avi) or Quicktime, where using an uncompressed codec within Ogg provides excellent cross-bitstream syncing, or the application may be designed around the Ogg media framework where storing data in an uncompressed Ogg codec makes encoding it later while keeping comments/etc is made easier.
For Codec Development
As we experienced with Ogg Theora development, there is a shortage of simple raw data formats which support the capabilities being tested in codec development. Additionally, the lack of inter-codec sync information (ie, when using .wav & yuv4mpeg2) for these non-Ogg raw formats makes debugging more difficult than it should be.
These uncompressed Ogg codecs will hopefully solve these problems, by allowing a wide variety of data formatting options and proper inter-codec syncing for testing and development. We should not be limiting ourselves to what existing raw formats support.