It begins the long, uphill battle against fat normalization.  When you see a fat girl in a dress at the prom- your fat-conditioned brain goes "ehh she doesn't look good but what are you gonna do"  but then you see the fat standing next to a thin girl in the exact same dress- you IMMEDIATELY recognize how utterly vile the fat is, and your thought goes to "God that is fucking horrible how did that thing even think it could show its face in public looking like that?" which is how it used to be before we started normalizing obesity.