Beauty products make all kinds of promises to their consumers, but how are they supposed to know if it's "working?"
When the consumer starts applying that facial scrub, they know it's working when they start to feel the tingle. That tingle is a little bit of peppermint that the makers put in these products. The peppermint itself is not an active ingredient. It won't clear out your pores, rejuvenate, or hydrate -- it's just there to make the active ingredients more impressive.
The same concept is applied to a variety of software products. Everyone loves a snappy experience when shopping, but if you are trying to find the best price on a flight or a clothing stylist that is just right for you, wouldn't you feel better if it took the machine a few seconds to really crunch the numbers before finding a match? Even if your highly-optimized system could have a result rendered to the browser in 100ms, it might be more enticing to the end user if it takes a couple seconds.
Consider the airline example. You could add an animated split-flap display, for a little whimsy, that lets the user know that you are hard at working finding the best flight for them. You might have a result sooner, but this bit of flare reasserts your value proposition and subtly tells the user that your secret sauce is hard at work for them.
To be sure, there is a bit of deception behind this technique. You should use it sparingly. With a little peppermint added in the right way, you'll help your users know that it's working.
I've only heard anecdotally of this technique being used. I'd love to find some documented examples of it. Reach out or leave a comment if you know of anything.
I've implemented it! In Rally's (now defunct) Choice benefits management platform, we had an data-import upload that only took .5 seconds to process, but we implemented a processing bar that took 3+ seconds - because users expected it to take time.— Nicholas Bailey (@nbdbailey) March 3, 2020