If you go onto rocky mountain sides and giant rocks near beaches for great sniping positions or overlooks, the Mesh on the rock doesn't match the texture.

So the player will either do one of the following.

1. Glitch into the rock and see everything.
2. Get stuck on the rock and be unable to move.
3. Have a great firing position just to find out that the rock has a invisible wall blocking the shot.
4. Slide off the rock/cliff and fall to their death.

So there is 4 good reasons why to re-mesh the rocks/cliffs so they actually work properly.

You can find these rocks/cliffs at, Airport overlook watch station, and all around the coast of the island.
They also appear on the map as mountain symbols.