What are the main differences to something like nethogs or iftop?
They are similar but they answer different questions. By default, iftop will tell you "this network interface on your machine is talking a lot to ycombinator.com". But you don't necessarily know which processes are doing the most talking collectively. This will tell you "Firefox process 4567 is talking a lot ycombinator.com" and you'll know whether 4567 is also one of the chattiest talkers right now.
But that's what nethogs does.