The first games had to put up with a global light source, with shadows and structures drawn-in. The changeover to 3D graphics gave objects more details and various different light sources generated additional shadows. As many objects are still made up of large surfaces, structures like grass, leaves or sand had to be painted on. If something like rails or stones are to stand out from the flat surface, then they need to be drawn in as proper 3D objects.
Pixel-based lighting means that it is possible to simulate a structure on a surface. Sand can be given waves, and the rocky wall can be given rough bumps. Within a texture, height information is saved as grey scales that are transferred to the surface in the form of shadows.
The simplest form of this is called bump mapping, where the height information of the grooves is just simulated. The surface remains smooth, and the geometry of the object doesn’t actually change.