I have done both foiled and non-foiled ribs. It seems many top cookers in BBQ competitions will use foil wrapping during the process. To me foiling gives the ribs a different flavor profile than straight smoked. I tend to prefer a non-foiled dry rub only rib with a mop (spray) of apple juice and vinegar as they cook. If I have my style for dinner, I choose non-foiled with no additional sauces for the finished rib.
My girlfriend likes a sweet glazed rib. When I do hers, I will do a 3-1-1 method (3 hr smoke-1 hr foil-1 hr glaze) and the ribs are finished off with a sticky finish. Seems most judges in BBQ competitions want this method for higher scores.
The big taboo, and it can happen quickly when foiling ribs, is to over cook them. If the meat falls off the bone...its wayyy over done and back to the drawing board for lessons.