Surface roughness affects friction in a very important way. As the smoother a surface the less friction, or forces opposing a moving object, will occur. For example: have you ever tried to slide across a tile or polished flooring in socks and find it quite complicated to stop. Try this again on a wooden tiled or like flooring, you will soon realize that it is much more easy (ifnot forced) to stop on this flooring.
How does surface roughness affect friction