Some of David's points are pertinent regarding HH cooks where no foil is used (easier to overcook; easier to overshoot temps; outsides done more than insides; more chance of the rub burning), and some more pertinent to cooks where foil is employed (less bark; less firm bark; less smoke flavor; less smokering; steamed/braised texture and flavor - though 'hammy', imo, is due to other factors and has nothing to do with HH or foil).
Bark texture is pretty easy to re-establish if lost during foiling. I don't bother with this for brisket, as the rubs I usually use end up sufficiently bark-y for me, but I do with ribs (I foil ribs sometimes when adding a flavor layer). Imo, (commercial) ribs at HH do not require foiling. They have neither the mass nor the fat-to-lean ratio to make it a must. Ribs I cook at 325-375. Cooking ribs at HH without foil means a rather narrow done window and thus more attention is required.
Smokering development is not difficult to achieve with HH cooks. Cold meat and a moderately slow ramp-up to cooktemps works well.
Though I don't care to cook butts at HH, because I do not like foiling them, I do cook them sometimes at higher heat - 275-300.
Per the OP, HH cooking, using foil, works well because cooking is much more efficient after foiling occurs. Unfoiled at the beginning is used so the meat can take on smoke, color, develop a smokering, develop rub flavors and texture. Cold meat placed into a cold cooker with a slower ramp-up also allows for enzymatic tenderizing until the enzymes cease activity as the meat gets warmer.
After foiling, the much more moist environment created increases heat transfer exponentially. Though not technically braising at the outset of foiling (unless liquid is added to the foil), a braising environment is created as moisture/drippings exude from the meat. This environment can mean much more even cooking of the meat. Rather than an oft-seen result of the thin end of a low/slowed packer being somewhat-to-quite overcooked by the time the bulk of the flat portion is tender, cooking in foil minimizes this because of the more efficient transfer of heat, and because the juices are contained. One can overcook anything in foil. If braising and taken to long past tender, at first, a pot-roast-y texture/flavor is often the result; further past that point, the meat eventually loses its ability to hold moisture and the result is essentially dry-meat-in-liquid. In most cases, however, the done window is sufficiently wide enough to avoid this.
