I use tracking all the time. I use the Perisno mod though but even then.
I use it, for example, to figure out if an area needs more patrols or not. If I see multiple tracks of different sizes belonging to different bandit parties, it probably means I need to clear some stuff out there and maybe put a lord on that fief. If I don't do this, then the fief won't grow in prosperity. If it doesn't get richer, it makes less money then it could be making. If it makes less money then I get less money. If I get less money I can't pay for certain things like units or upgrades. I still can pay for them, just less. If a lord owns the fief, he gets less money so his party is smaller because he can't hire as many troops. (Yes it is decided by how rich the lord is it seems.)
A day or two after a war declaration I pay more attention to the tracks in my territories. If I see a fat track or war party track, coming from enemy lands, it's probably a raider. Pitiless, debauched and other bad lord personalities will go off raiding by themselves. You'll notice the same few dudes constantly raiding your stuff. If I see their track, I follow it or I send someone there to deal with it. That's one lord by himself. The way I understand it, the more lords you defeat, the more morale drops the enemy kingdom gets, the closer they get to declaring peace. So one lord by himself is a cheap and easy blow to their morale. This guy now has to go and recover and my lands are protected and churning out money to get more and better troops.
I'm not sure if this is in native or not but sometimes you send stuff out and it gets captured by a bandit group, so I track the group. Maybe a better example: my lord gets defeated and captured near an area. I go there, find the X on the map. The X means battle. Whatever arrows go out of this x will have my dude as a prisoner. It's easier to defeat a prisoner holding party in the open field than it is to besiege a castle or go through the hassle of breaking them out of it. This lord now likes me better, I have this lord in the field (after he recovers) so his party will add to enemy war damages or prevent war damages on my lands.
You see, tracking is a vital skill to have when need to work with the deep intricacies of the game. When playing on maximum hardcore difficulty or even average difficulty. When money is tight, wars are plentiful (I got attacked on 5 fronts at one point) and you need to choose your actions carefully. When the game becomes about specific choices, that's when it gets epic. Not just "get full cav army and steamroll" but "do I siege this castle and let my fiefs be raided... thus losing money and a long period of no recruits from those fiefs, or do I leave this castle for what it is, protect my fiefs, but not take the castle, not give the enemy lords negative relation with their king and thus creating quarrels that lead to internal struggles,... or do I ignore both these and go for something else?"
You see, taking a castle means you take away fiefs of one or more lords. If the castle belonged to lord A and it had a village belonging to B, then I take the castle and neither A and B have fiefs (unless they have more than just those). Fiefless lords get -1 with their king per day (or is it -3? Whatever they start complaining at some point). Then, when the king gives them fiefs after all, the king loses relation with all the other guys who didn't get a new fief.
When you understand these intricacies, you now realise that taking a castle just to let them recapture it later, means you're stoking a feudal fire that makes the lords of that faction start hating each other. Their unity drops and you'll see smaller campaign groups because they don't want to cooperate with each other. This means easier small open field battles which your lords or you yourself can easily win.
The tracking skill plays a major role in this and that's why I have a dedicated tracker going 10 on this every time.