Hypothetical Situation - What prevents someone from accepting at two of the schools they've been accepted at? They want a decision, but it's not a contract. Playing devil's advocate, if they're not willing to commit to assistantships or other support until later in the year, why should I have to decide now?
As I see it, the potential downside is in 'burning the bridge' at that institution - If I decide not to go at the last minute, then they probably would never consider me in the future.
What it *does* do, however, is deny that slot to another candidate who has been waitlisted.
Now, as a part of my personal ethics, I'm not comfortable doing this. Still, the thought *did* cross my mind. Several times.