Funny how it works:

Times are good. There's inflation with cash.
Times are bad. There's inflation with cash.

But the big difference I see between inflation and devaluation: People talk about a quantified degree of inflation. It can go up or down, it can be high or low or ver low, but it's pretty much never 0, which it would need to be to say that there is "no" inflation. People don't just say "there's inflation again this year", they talk about how much of it there is.

But hardly anyone ever quantifies devaluation. Are you really scared of 0.2% inflation, or only of something like 50% inflation? Well, should you be scared of all devaluation, if you have no idea of how it's quantified?

I've been collecting miles and points for close to two decades now, and I'm hard pressed to find cases where devaluation has been that high cumulatively at most programs over that time. Occasionally when a program changes radically (Southwest going from credits to points, Delta going way beyond chartless quite a few years ago) devaluation can be more sizeable, but in most cases it's just a semi-steady march, just like inflation is.

Meanwhile, I don't know if it will continue (it's already slowed down for many due to banks' anti-churning measures), but the ability to earn miles through non-flying grew at a faster pace for many years, in many programs, than the value of those miles devalued.

But if you can't earn that fast any more, that brings up another question: Will the miles you have devalue so much that it's not worth hanging onto them (but only worth it to "use them up" at a poor redemption value)? Ie, you have to compare the amount of devaluation to the poorer redemptions you can do right now, to evaluate that question. But if all you know is that there's devaluation, but you can't quantify it, how can you make rational decisions about how to react to it?