Amazing Ribs has a great page on meat temperatures. Explains all the science of what happens to meat in the smoker.
Basically as the temperature of the meat climbs the water reaches a point where it is evaporated, or "sweats" out of the meat. That's the stall. The "wetter" the meat, the longer the stall at any given chamber temp. Water is what gives meat juiciness at low internal temps, like steaks, beef roasts, pork loins, etc where you heat to a max of 145F. Meats you take to higher temps get their juicy succulence from another place.
Butts, shoulders, briskets, chuckies, are tough cuts of meat with lots of fat and connective tissues. Fats render out at lower temps but can take a while to render completely. As the internal temperature of the meat climbs past 170F, that's when the tough connective tissues in the muscle start breaking down and melting. By the time the meat reaches internal target temps of 200-205, the connective tissue has melted and made the meat juicy again.
Now, I wrap soon after the first stall starts. Here's why:
First, I wrap to capture that liquid evaporating out of the meat. Water conducts heat 25 times faster than air so the moisture trapped in the sealed wrap will cook the meat faster. Scuba divers have that fact drilled into them. If you doubt it try this little experiment. Walk outside barely clothed when it is 50F. You notice the cold and will chill over fifteen minutes or so. Go warm up while filling the bathtub with 50F cold water, then jump in. It takes your breath away it feels so cold! Your body temp can drop to dangerous levels in a matter of minutes in a large body of cold water as the heat flows rapidly out of your unprotected body into water compared to how fast the heat flows out of your body into the air.
Second, I want to capture the connective tissue juices that drip out of the meat. I use it for au jus and for cooking other things. Those "drippings" are pure flavor. Have you ever wrapped a meat you cooked to a high internal temperature, stuck the leftovers with the juices in the refrigerator, then noticed gelatin the next day below a layer of fat? That gelatin is the melted connective tissue from the muscle of the meat. Flavorful, FLAVORFUL stuff.
With wrapping you give up the crispy bark, but I get so much more use out of the juices and gelatin. Plus I'm saving time. Once I wrap I let the smoker temp climb because it is no different than putting it in the oven since no smoke can be absorbed by the wrapped meat. Basically the meat is braising in its own juices.
I last did an 8.5 lb pork shoulder for pulled pork over the holidays. I used 275F chamber temp or so, then let it climb to 290 or so after I wrapped. It was just over 8 hours from meat load to dinner including the unwrapped smoke, wrapped cook, and rest period. Succulent, juicy, and oh so flavorful.
That sir, is why I wrap.