I think there is a big misconception about drawing with precision. A lot of people think it leads to drawings that look over rendered or “tight.” I can understand how they think exactness leads to harshness, but it’s not true. Overly tight drawing is not a precision problem, it’s a lack of seeing problem.
If you feel your drawings are too tight and that you need to loosen up, I’d like to suggest that you try to draw with even more precision instead. Look closely at your shadows and highlights and see if you’re drawing them as they really look. In most cases, you’ll find that you’re making assumptions that aren’t true. Look for soft and hard edges in even the tiniest details. They are there! You just need to look close enough.