Chicken is the protein it makes the most difference on IMO. I've had some great results on lobster tail as well. Also, being able to have a 5 lb chuck roast that is medium rare pink all the way through except for the outer crust really changes the roast beef sandwich game. You can also cook a burger to rare and hold it for a long enough time that it's pasteurized and safe to eat. Making yogurt and creme brulee is pretty cool too, even though it is just a different process without any significant difference in result.