Help me understand water filtration (water pipes)

There are a lot of different designs out there in regards to water pipes and filtration. Some utilize tree-percs, some use shower heads or shower caps, some utilize both in different sections of the tube. Some have 4 arms and I've seen some with as many as 24 arms. Fixed stems or diffused stems, what does this all do?

Is there a science to this or are all these designs doing the same thing? At what point are these designs overkill? When are they not enough?

i have a triple perk double diffused bong and it think it's way better than a single perk not diffused bong