I’m currently on a Delta flight that I paid for eight years ago, in 2017. Well, more specifically, I bought a gift card for the flight using an Amex Offer back then; if memory serves, I paid $240 for a $300 voucher, saving me a cool $60.
At the time, it seemed smart: I’d flown Delta/Air France once or twice in the preceding year, and a 20% discount is pretty dope.
So, sounds great, right?
Nope! Back in late-2017, VTI was trading at $121/share. My $240 would have bought me about two shares. Today, VTI trades at ~$320, which means my $240 would have been worth closer to $640 — enough to nearly buy a roundtrip TLV<>JFK flight on its own (I redeemed some miles on my Venture X).

By holding onto the gift card as long as I did — due to a pandemic, a war in Israel, and a gradual shift to United Airlines — I gave up on a ~2x return.
Moral of the story? I’ll keep buying gift cards — but only for redemptions in the near term.
And if I do make a less-than-savvy financial decision, I’ll at least write a blog post about it at 40,000 feet.