I am just simply baking the base color of my mesh into an image. However, the baked image is noticably lighter by around 10%. Why is this the case?
A slightly easier way is to connect the color socket you want to bake directly to the Material Output, and bake the Emit type. You also don't have to worry about unchecking Direct/Indirect.
This works because when you connect a color socket (yellow) to a shader socket (green), it's as if there's a default Emission shader node in between.
The same method will work for a "dumb bake" of any color socket of course, not just Base Color. (If you want to dumb-bake a scalar instead, try putting it in a Principled's Roughness socket and baking the Roughness type.)