Holes allow the natural juices of the meat to run off.
Any good marinade will be slowly adsorded by the meat. This is way most good marinades require overnight in the frig to properly favor the meat. There are numerous great grilling cook books available as well as some books dedicated to cooking meat. My favorite is a book by the Lobel family that run one of the supposely best butcher shops in Manhatten. I saw these guys on the the food networks Cooking Live.