mstyrcz

The main reason of using 2♣ with weak 5-4 hands is that in Polish Club you can open 1♣ with a very strong hand. Any jump after opening 1♣ is forcing to game and means a good suit. You can't jump in 3♣ even with a quite strong hand. So sequences like 1♣-1NT-2♣ would be problematic for your partner if you could have 12 points and 17 as well. When you use Precision-like 2♣ your partner can be sure that 1♣-1NT-2♣ means at least 15 points.