well if it's sketchy it's actually harder to make out details so when it's sketchy details are implied. If you want lots of details then it's better to do a clean drawing. Try doing ornate armour sketchy style and then you'll see that it gets rather... messy. Believe me I've done it before and it's not cool. :(
But I still like sketching anyways, so I just don't do lots of details or ornate armour. | 
