Simple. Makes his transaction more important that others of lesser value. He wants it done and done now!
That doesn't really make any sense. A transaction is confirmed in blocks, and as I see it there is no differentiation between one that pays and one that does not. Unless the discoverer of a block can explicitly state "I don't want to confirm a transaction unless it pays me > xx BTC in fees" then all transactions will get confirmed at the same rate. Is that the case?