What is the relevance of the centum-satem isogloss?

The centum-satem isogloss refers to the distinction between languages that evolved from the Proto-Indo-European palatovelar consonants in different ways: some retain the sound as a "k" (centum languages) while others shifted it to a "s" sound (satem languages). This linguistic division helps trace the divergent paths of Indo-European languages and is important for understanding their historical development and relationships.