flying for status can make a difference some of the time. If your status gives you double miles, the value of those miles (for reward tickets during peak times) is worth more then what it would cost to buy those tickets.

Two round-trip tickets to Europe in the winter will cost you (during sales) no more than $800 total. The miles earned on this translates into a peak award ticket to Europe in the summer that would cost (to buy) much more than the $800.