what does a valve grind do?
 

ok so i had my good friends mechanic do my heads...he put in new seals put on my comp cams springs jet washed the heads painted them and did a 5 or 6 angle valve grind....what does that mean? what does a valve grind do? he charged me 200 for everything...ooohh forgot he also milled the surface to make it flat again..but what does a valve grind affect? am i going to get any better performance from the grind?