Don't know that I'd call it "pros and cons" necessarilly, it just depends on what you're into.
Foiling makes it easier to achieve consistent results. Like Piney said, braising the meat and making it nice and tender. It also helps speed up the cook somewhat on briskets and butts. But it tends to make the bark mushy as Eric stated so if you like a firmer bark, taking it out of the foil to firm it up on the grates may be a good idea. I do this with ribs but not butts or brisket.
Great results can be obtained both ways, at least from the Qviews I have seen, but I find that doing it without foil is a little tricky -- at least for me anyways.