if most of your picks play then you have a good scouting staff. It means every year, you dont have to spend money on a ufa to replace a 3-4 liner because you can fill that need internally on the cheap. Plus, with most of the picks making it, there is a higher chance that one of them will become a star.
Exactly, people don't get excited about 3rd and 4th liners, but having young low salary ones available from drafting is a luxury many teams would like. The difference between having Max Lappiere, Greg Stewart and Matt D'Agostini around on low end contracts and having to sign vet UFAs like Radek Bonk or Mike Johnson (or Georges Laraques) is millions saved, which adds up. That pays for an extra premium guy to be squeezed in (Lang or Tanguay).