What does the Tracker hireling’s Track skill really do?

In Dungeon World, there is a hireling skill-set called Tracker. It has two skills: Track and Guide. Guide is straight forward. However, Track doesn’t make much sense to me as I’ve never been good at understanding what Ranger-type classes were really good for. (I’m a city slicker; what can I say?)

The description for the hireling skill Track follows:

When a tracker is given time to study a trail while Making Camp, when camp is broken they can follow the trail to the next major change in terrain, travel, or weather.

What does it mean to follow a trail to a change in terrain, travel, or weather? Wouldn’t a change in terrain be obvious?

Dude: “Hey, look a mountain to the south-west.”

Tracker: “Hmm, yes, to reach a mountain to the south-west… we must travel, SOUTH-WEST!”

A change in weather?

Dudette: “Wow it sure is pouring rain! The clouds to the north seem less dark and rainy and the wind is clearly blowing south. I wonder which way we could possibly go to avoid this downpour.”

Tracker: “Hmm, I see you are in need of my specialized skills… if it is raining here, it is not raining to the north, and the wind is pushing our storm further south… we must head… NORTH! Yes, aren’t you glad you pay me?”

I don’t even know what a change in travel is.