The first big advantage to intensive learning is pure chronological frequency; in other words, you're learning the language more often. You know that feeling when you know you have the perfect situation to use the new verb you learned in class, but you just can't recall it? That doesn't happen in intensive language learning. With a shortened cycle between classes, each day gives you one, digestible chunk of new information to play with. It is much easier to practice (and therefore internalize) five new verbs with class time each day to ask questions, than twenty new ones and have your questions put on hold until next week.