It is for both collecting and re-selling reasons. In fact, it is a good investment from the point of view of a collector who can have a great variety of Pokemon cards from a set. Moreover, considering that the price of a single booster pack is around 4$ (manufacturers suggested retail price MSRP), you can buy a Pokemon booster box for less than 99$ (with a saving of about 40%, in fact 4 x 36 =144$).