There's a lot of information to be learned by observing the payments flowing through a routing node. By having eyes on every payment, over time you will build up intuition about which routes are important to your node.

Eventually you will spot patterns and then the fun starts in figuring out how to increase (or decrease!) the probability of those patterns occuring. It can be tricky to spot those patterns because cause and effect are not obvious and seem decoupled without the right intuitions.

This is the core concept of running a successful routing node.