Work out what your SkyMiles are worth on a specific booking, and whether redeeming actually beats paying cash on a program that prices almost everything off the fare.
Delta abandoned award charts some time ago and prices its own flights off the fare, which pins SkyMiles into a fairly narrow value band with little room for a spectacular redemption. That is not automatically bad. A near-fixed currency is predictable and easy to use, and it never leaves you hunting for saver space that does not exist. It just means the strategy is different: spend them when the rate is acceptable rather than hoarding them waiting for a sweet spot that the program has largely engineered away.
The better SkyMiles redemptions are generally on SkyTeam and other partners rather than Delta's own aircraft, where pricing can be markedly more reasonable for long-haul premium cabins. Delta's own search does not always surface partner space cleanly, which is a large part of why people conclude the program has nothing to offer. Award Travel Finder will show you what is actually bookable before you write the balance off.
Delta periodically runs promotional award pricing on selected routes and dates, and these are genuinely the moments when SkyMiles punch above their usual weight. They are short, route-specific and easy to miss, which is an argument for having a rough idea of your target trip in advance so you can recognize a good price when it appears rather than working it out from scratch under time pressure.
SkyMiles have no expiry, so there is no deadline forcing a bad redemption. The flip side is that a currency pegged to fares tends to drift downward in real terms as fares rise and earning rates do not, so sitting on a large balance indefinitely is its own slow loss. Amex Membership Rewards transfer to SkyMiles at 1:1, so topping up is easy, which is another reason not to keep more parked here than a planned trip requires. Check the transfer bonus tracker before you move any across.