Depending on how complex the thing is you might split it up into multiple pieces, take for instance a character, usually the head is separate and has its own texture.
But also it’s not complicated to make a material that can have several types of things in it–like clothing that has fabric, leather, and metal parts. You just have to create your textures correctly, that’s what the slots are for–diffuse, specular, roughness, metallic. You can change those values in your textures to get different materials within a single material.