[Martee]

I'm sorry but IMO anything that digs into the surface of the ball can definitely affect spin. I think everyone knows that spin does effect distance, if not then launch monitors wouldn't care to monitor it.

Well according to the USGA testing, irons smooth faced and groove can impart equal amounts of backspin. Noted by the USGA is that smooth faced surface may be less more difficult to accomplish or be consistent with, but none the less can do the same.

Spin has more direct effect if I recall correctly on trajectory and curvature. Obviously this will effect distance but there must be other factors to consider.

The notes in the In Search of the Perfect Swing was

5 iron smooth /grooved
avg speed 144.7 / 144.8
avg spin (revs per sec) 77 / 84
avg angle of projection 12-8 / 12-6
avg carry yds 155 / 154
avg run 31 / 27
avg overall distance 186 / 181

7 iron and 9 iron had very similar results except the spin rates and angles were just about the same. Distances were within a yard or so.

I realize it seems to be logical that the grooves should add, but in reality they do very little unless you are in the garbage, and that is where they allow for the water, etc to get out of the way of the ball to meet the clubface.