Quick normal question

Trying to bake to normals, following the wiki tutorial. theres a button called “get normal values from rgb image” in the texture tab (not the nor button in the map to tab), it says press this, but i get quite different results if i dont select this.

is this correct? cos un selected looks to give sharper results, but I dont really know what im looking for.

I baked a sphere with sub surf to a cube.

I think I answered my own question. I tried something different. with “get normals from rgb image selected” it uses the normal map to reflect the specularity.