They ensure what’s needed gets from Point A to Point B.
It might not come through in one large packet, because that is not always feasible, instead, it could be a grouping of multiple packets where Point B then has the harder job of reassembling everything broken out by Point A to make sure it could all gets there, all be delivered, but would require some extra work to put it all back together and see the big picture.
Networks are complex and with all these myriad of packets floating around, stuff gets lost, and corrupted so when it gets to the destination it’s not what you thought and you have to go back and ask for until you have the complete picture. And only then when you have the complete picture do you make a decision.
That’s what makes networks so great, they don’t make the call until they have everything in front of them, they look at the big picture, not the minute metrics to calculate success.
That’s what networks, all networks need to be.