Tight-fitting means that something sits very close against the thing it covers, with no loose space. It is used most about clothes: a tight-fitting dress, tight-fitting jeans, a tight-fitting T-shirt — clothes that follow the shape of the body instead of hanging away from it. It is also used about lids, doors, windows and covers, where 'close against' matters for a different reason: a tight-fitting lid keeps the air out, a tight-fitting door keeps the cold out. So the same word carries two feelings depending on what it describes. About clothes it is mostly neutral or even a compliment about style; about a lid or a door it is straightforwardly good, because the point is that nothing gets through. Notice that it is a description, not a complaint. If clothes are too small and uncomfortable, English speakers usually just say 'too tight' rather than 'tight-fitting'. Tight-fitting suggests it was meant to be that way.