Suppose you are playing 15-17 1NT openings, and you and your partner have never talked about what to do with 14 1/2. Now you are looking at a balanced hand and 15 HCP, but your hand counts to 14 1/2 using half-points. What should you do? Technically, you are too weak to open 1NT and too strong to open 1 of a minor and rebid 1NT.
A reasonable solution is to go with the field unless your correction is off from the field (who are not counting half points) by a full point. So, with 15 HCP and 14 1/2 HHCP, you open 1 NT; with 14 HCP and 14 1/2 HHCP you open one of a minor.
However, that means you make two different bids with what are essentially equal hands. That can't be good for partner's intuition. A half point probably doesn't matter much, so this is not a serious issue. Still, partner will be in the situation of his aggressiveness sometimes working and sometimes not, and unable to distinguish that you are bidding the same value hands in different ways.