Volumes of different density will cause the shock to slow at different rates and we end up with a twisted, knotted filamentary structure . The filaments seen are probably just the portions of the shock front seen edge-on from our line of sight. Through the examples above we have seen some of their manifestations. But they really serve a function of creation, destruction and mixing in the cosmos. This contributes strongly to the kinetic energy and heating in the galaxy and is, if you will, a sort of tilling of the cosmic soil.
Enriched material is dispersed from supernovae and molecules from clouds.
Without this kind of mixing, life on earth would undoubtedly never have arrisen. Through the condensing effects of a weak shock, material becomes dense enough to cool and form molecules. Slightly stronger shocks will ionize certain species facilitating ion-neutral pathways to molecule formation. This denser material on a larger scale also leads to gravitational collapse and star formation. Stretching the analogy a bit further, this is the planting of cosmic seeds.