UPDATE : a AMD removeu esse recurso da sua configuração mais recente do CCC (no momento desta atualização)
Resposta original:
I have asked and read answers on many multimedia forums, including AMD.
For what I have understood, these allow applications to be able to use the video card's hardware acceleration when decoding and encoding.
Also, it seems that programs that use the Windows Media Foundation, like Windows Media Player would be able to benefit from the hardware acceleration.
About transcoding, Windows has the feature to convert incompatible files when dragging and dropping them to a portable player that is able to use this feature. It seems this helps, again, to use the video card's hardware acceleration.
According to the Administrator at Codecguide.com (the official home of the k-lite code pack) these don't affect in any way other codec packs.