We ran a post earlier today suggesting that using frequent flyer points for upgrades often makes more sense than using them to buy flights. That can often apply -- indeed, I've advocated it myself in the past -- but it doesn't trump the ultimate rule of using frequent flyer points: there is no single rule that works for everybody, because everyone has different needs and opportunities.
I made that point the last time a reader asked me which scheme offered the best returns, and what I said then remains true:
We’ve always stopped short of a comprehensive “this is the best value” guide for one simple reason: there are far too many personal variables to make it possible to be comprehensive.
My own experience underline that. When I wrote that post, my main use for excess points was for upgrades. In the past six months, however, I've had a bunch of occasions when I have needed to book a flight on short notice. In that context, using points to get a flight cheaply rather than paying $400 for a one-way trip makes a lot more sense, and means I earn more from each point. (A factor here is obviously the availability of seats, but the same applies to uogrades.) In six months, my requirements may have changed again -- but the only way I'll know is through careful analyis.
The key lesson is to think carefully about how much it cost you to earn those points, and spend them in a way that gets maximum value based on your current situation. That will differ depending on your own needs and wants, but it won't happen without a little planning. Applying a blanket rule won't ensure you get the best value.