Others choose to live on-campus in dormitories, but the drawback there is that many on your floor have dissimilar majors and interests. Interest houses bring together people who are in the same field of study, so that study partners and test preparation become easier. To compare notes from someone in your class you simply walk down the hallway. Underclassmen benefit from the experience of upperclassmen who have had to face decisions on everything from class scheduling to major and career planning. You don't have this opportunity in a basic dorm setting.
Social enrichment is just one of the many fringe benefits from living on an interest house floor.
Planned socials, intramural sports, weekly floor dinners, and other activities help cement friendships and help the floor grow from individuals to a community.