it's best not to rush a player. unless you draft a college guy who's 75% near his ratings already or sign a IFA that's similar just about every prospect is gonna need at least 3 years at the minor league level before you can bring them up and not hurt growth.
most prospects won't reach their projected ratings but you wanna give them enough time to marinate and get properly seasoned.
me personally, i don't care how good a prospect starts out. he goes to rookie and doesn't come up til he's gone a season at rookie,low-a,high-a & then AA.
i may skip AAA if he's good enough but 4 seasons is the minimum i like my guys to have before bringing them to the majors.
everyone above is right about the range factor though. just because a player doesn't make a ton of errors doesn't mean he's not costing your team. those balls that are just out of his reach or that he just couldn't get to turn into singles,doubles, those turn into more pitches for the staff to throw and that could allow for those crooked number innings.