Like William said, it depends on intent. For instance in most Catch and release tournaments for large fish, when the leader touches the tip top or the mate or guide grabs it, that fish is considered "caught." They generally award a token point for retrieved flies just so everyone doesn't cut the leader at the first opportunity just to save time.
For me, an 8-15 lb. dolphin, for instance, isn't considered caught till it's in the cooler - unless I already have one in there, then standard tournament rules apply.