When you put your lunch in a Thermos or one of those padded, insulated lunch bags, the intention is to keep that lunch at its original, intended temperature. If you put it in the bag cold, it should stay cold. If you put it in there warm, the idea is that the insulation will keep it warm. Simple.
But if you put it in the insulated bag and then place it into the refrigerator in the faculty lounge, it's really taking up more space than necessary. In fact, if you're putting it into the refrigerator, the goal is to keep it safely cold until you need it for lunch...so why insulate the food from the cold temperature of the refrigerator?
See what I mean? It doesn't make sense to put something into the cold compartment of the refrigerator and then insulate it from the cold! The bags in our faculty refrigerator end up taking up so much more space than is necessary, and that's just inconsiderate.
But you haven't thought about it that way, have you?