I wrap neither really tight nor really loose. Usually, I'm in a hurry to get a hot piece of meat wrapped and back in the cooker, so my primary goal is just to get it sealed. I've never had any problems if any sort doing it this way, but I only foil on rare occasions.
Weber Smokey Joe
18" Weber Kettle
22" Weber clone kettle
Curb-foundling char-broil gasser
WSM: Assembled! First cook: 8/25/06
Fanatical devotion to the Q