Mies & Cash is usually by far the worst way of using miles, and only makes sense if miles would expire otherwise and cannot be used for an award ticket or upgrade as not enough. A bunch of carriers now seem to charge nearly as much (if not more, check out LH Group at times) in surcharges and taxes on award tickets as the total cost of a revenue ticket is; this makes little sense, given that fuel surcharges and taxes should be the same! In these cases it may make more sense to book a revenue ticket and then upgrade with miles, depending on the carrier (but most carriers try to stop this by charging much more miles for upgrades than an award ticket would cost, e.g., LH Group again).