When Draco returned home in the summer after the miracle of being let off a prison sentence, he had warded off the main drawing room. The pain of watching Hermione be tortured there by his own Aunt was enough to make him feel sick. By warding it off there was no longer any risk of accidentally walking in there or having guests enter and discuss it. Any reason he may ever have to go in there was now eradicated by his actions which he was very proud of. 