The point is very similar as it is with belts vs. trains. In normal gameplay belts could provide more than enough throughput realistically versus trains. When you scale, you want modular setup and trains do that. You absolutely do not want to put pipes into every possible direction and you also nee...

So fluid wagons and pumps are pointless. Next step is to make chest share one infinite storage to get rid of a trains. After all it's a very confusing mechanics for new players, a big nono for a casual game like factorio.