Why normal stretching distorts
Stretching a whole image to a new shape scales everything by the same factor in one direction — people get wider, text gets fat, circles turn into ovals. That's fine for abstract backgrounds and terrible for anything recognisable.
Edge stretch works differently: the photo keeps its exact pixels and only the outermost row or column is pulled outward into the new space, blurring a little more the further it goes so it reads as an out-of-focus continuation rather than hard streaks.
When to switch fills
Stretch is perfect for plain studio backdrops, gradients and skies. For textured scenes (grass, brick, water) choose Smart fill; for patterns choose Mirror.
