i've been doing that ever since i started playing golf. but i really only did it to clean the clubface... the resulting ball mark that was left was like a by product and it helps you line up your drives so you know if your too close to the ball or too far away.... and if something goes wrong you can generally tell why.

not so much with irons, but sometimes it leaves a mark.

my new irons are so forgiving - Taylormade RAC OS2 - if i hit the outside of the club the ball will still travel straight, feel harder through the club but remains straight. i'm loving these, only had them 2 weeks