Despite the poor general value, there are specific scenarios where purchasing is tactical:
You are often paying nearly three times what the miles are worth. For a full ticket, it is almost always cheaper to pay the cash fare directly rather than buying the equivalent miles. When It Makes Sense to Buy can i buy delta miles
How to Buy, Gift, Transfer or Donate Miles | Delta Air Lines Despite the poor general value, there are specific
Using miles to upgrade to premium cabins (like Delta One) can sometimes yield a higher "cent-per-mile" value, potentially making a small mileage purchase worthwhile. Gifting and Transferring Despite the poor general value