First, let’s define a few terms. Texture is a 2D image. Mapping is how a texture is applied in the shader’s calcultaion. Textures made for a specific type of mapping is usually referred to by the mapping type. Like a normal map, AO map, shadow map, etc. The shader is the part that determines what types of mapping is available and handles the calculations for a material. EEVEE and Cycles can combine different shaders for a single material.
Second, If you have a complex node setup for a material like textures(Images) layered on top of each other then you can bake them to a single image texture. Same is true if you have a procedural texture node setup. This simplifies all those calculations and steps into 1 image. If you’re already using a single image or you are painting directly on that single image then there is no need to bake. A common texture to bake is normal maps. The most common situation(Not the only one) is if you have a high poly count mesh and a low poly count mesh and want to make the low poly look like it is the high poly count mesh, by baking those details to an image. This is quite difficult to try and paint those kinds of details manually.
Hope that helps clear up some things
