Texture bake doesn't match viewport EDIT - new pic attached to bottom
I've got a billion nodes making a texture that covers most of the robot.
i want to animate it tho, and the poota chuggs even when moving things around in viewport, so i believe baking the texture on to each mesh will free up processing power.
(i have another post up regarding animation misery)
baked image size is 2048, tile size 2048, 64 samples. Object has been unwrapped and looks good when all the nodes are plugged in.
the resulting diffuse is f*&amp;#ing awful tho.

I cant see what i did wrong
on another note, all the youtube vids suggest exporting diffuse/bump/aoc etc seperately. why not just use combined? - see answer below
UGH.. so, i found i was unwrapping the wrong hip (local camera in uv unwrap pointed at the wrong hip). the poorly setup AOC was prolly making it darker than expected, and i had overlooked the metallic in the rust part, mixing with the rest of the bake.
But. still no love. why is this happening. the rust just goes crazy in soem faces. its def a new correct uv unwrap, which displays fine until i bake
Your issue is, you baked only the &quot;diffuse: color&quot;, which is only the raw color that the render engine is supposed to use, in addition to other shading infos, to create the final result. If you want the final result, you need to do another kind of baking.
Now the question is, do you want something static that doesn't react to lights, or do you want to keep your model's surface reactive to its surroundings?
If you want something static, make a &quot;combined&quot; baking. It will bake the final result into one texture file. Be aware though, it really does bake the &quot;final&quot; result. Which includes

little shadows created with the lights bouncing on your bump maps
global illuminations
reflections
subsurface scattering

All will be baked and fixed in stone inside one map and nothing will adapt anymore. It will turn your model into a painted statue.
If however you want to keep your model's material simple yet dynamic as it should to its environment, then you need to basically bake the raw data that should be plugged in a principled shader. Which basically is:

albedo data (raw color without shadows)
metallic data if any
specular
roughness
bump / normal / displacement data

And so on as you need.