I plan my purchases before hand by checking on release dates.
But if I see a popular title that I want and selling cheap enough in Greenhills (most likely used), I immediately scarf it up. Cause it'll probably vanish in a day or two if I leave it there. (Bought a used orig PS2 copy of RE4 for 300 pesos on impulse the other day)
The only things stopping my purchases is whether or not Asian version lang ang binebenta. I have to ask around and research on pros and cons (if any) kung aandar ba yang Asian version sa U.S. 360 unit namin, kung compatible for multiplayer (with PSP games) with friends I play with, kung compatible ang DLC with my U.S. account.