Baked Lights Don't Work When Ambient Occlusion Is 0

Unity 2020.2
URP

I was playing around with a shader graph and found that my materials were only visible if I had realtime lights in the scene. When I used baked lighting only, the textures were completely black no matter what I did.

Eventually I realised that at some point I had set the ambient occlusion property on my shader graph to 0. Changing it back to 1 made everything work fine, but I'm just trying to understand why this is the case.

Is it just that this parameter of the shader is expecting a texture map (like a normal map) rather than a numeric value, so setting it to 0 is basically telling it the entire map should be in full shadow?