lighting yes, but that's not all. many 3d apps offer the opportunity to define a texture just by a handful of parameters ("procedural texturing"/c4d calls it "shaders"), which produce no texture seam and always tile perfectly. you have to write the result into a bitmap ("baking"), otherwise the texture cannot be exported. multiple texture layers, e.g a transparent logo on one of the wings of a space ship can also be baked to prevent the engine to calculate 2 texture layers.
and: some modellers use multiple giant bitmaps (2000²+) for their models. baking the texture makes the bitmaps fit in a predefined size (128², 256², 512² etc.), just using the parts of the images which atre really needed.
