Because: (1) If you buy a ticket directly, 72*8=576 yuan.

(2) If you buy a ticket, it costs 72*6=432 yuan.

(3) Group purchase saves 576-432= 144 yuan compared with direct purchase.

In this way, we can directly compare (1) and (2), and we can see that it is more economical to buy group tickets. Save 144 yuan.