Tried a 4-hour rest in a cooler last weekend. The difference was insane. The brisket was so tender it practically fell apart when I picked it up. Every single slice was juicy, no dry spots at all. I'm never rushing a brisket again.
Oh absolutely, it's a total game changer. I used to just let it sit for an hour and thought that was enough, but after trying a long rest like kim373 mentioned, I'm convinced. That extra time lets all the heat and juices spread out evenly so every single bite is good. It turns a decent brisket into something you can't stop eating.