Placing the contract in exactly the right place is like parallel parking. You have to mentally judge the size of both the vehicle and the space. In bridge, you have to mentally judge the size of the hands, and park in the right sized spot.
Once one of the partners has LIMITED his hand, the partner of the limiter is now in a position to "Do the Math" and place the contract. For example, you open 1♥ and I say 1 No-trump. You know I have limited my hand to exactly 6-9 pts, and you can add that to your own. Below 25 pts combined? Partscore. 25-plus? Game.