>>366825941
An example would be an emission map. If you're using one material with a 4k texture, then you'll need another 4k texture that is almost entirely black for the emission map. With two materials, the emissive material can use two much smaller textures that aren't mostly wasted space. If you use transparency, it is better to only have the transparent faces on that material to avoid having faces that don't need transparency at all being rendered with an overly complex shader.