A few degrees either way just "rocks" the power curve a bit.
Advancing the camshaft reduces maximum power a bit but increases low rpm torque. Retarding the camshaft increases maximum power slightly at the loss of low rpm torque. Usually cam manufactures add around 3 degrees advance into the cam so you can install it "straight up" without the use of offset keyways etc.
A mate of mine was having probles with his engine combo and I took 3 degrees off the 4 degrees advance. So that left it 1 degree advanced.
Don when on a great length about how "retarding" the camshaft would do this and that and that was why it would not run right. Nothing to do with all the mis-matched parts the guy had and a Demon carb that runs rich without 20 degrees initial then.