There's definitely something to the juiciness though. What Swimpy says makes sense.
My husband was a far more accomplished cook than I when we met, but when we met he was also a vegetarian, so we've both had to learn to cook meat. For whatever reason (strange ovens or over-checking -- I think the latter) -- meat always seemed to take longer for me than indicated by the recipe, so I'd tend to have to rush it to the table once it was edible. I knew about the "rest" thing but thought it was just sort of frippery, can do without it.
At some point I got the hang of cooking meat, and started letting it rest just because it would be done but I'd still be fiddling with the sides or whatever. That definitely made a huge difference, for the better, and I make sure to let it rest now.