CAS sliders will only take a sim's body so far. Vanilla Sims 4 bodies converge on the same two or three silhouettes no matter how long you drag, because the sliders move a handful of regions and leave the rest alone. Body presets fix this at the mesh level: one click in CAS and the whole body shape changes — hip-to-waist ratios the sliders can't reach, shoulders that actually vary, soft bodies that look like people instead of mannequins.
This collection pulls together 130+ body presets across the full range: curvy and plus-size presets (consistently the most-downloaded category), athletic and muscular builds, male body presets — chronically under-served in CAS content — and the subtle "slightly more realistic than vanilla" presets that you'll end up applying to half your saves. Presets are also the cheapest diversity tool in the game: a household where every sim shares the same body reads as generated; one where bodies actually vary reads as written.
Two tips before you download: presets stack with skin details (a body preset plus a skin overlay is the standard realism combo — see the skin details collection), and most presets are found under the body type icons in CAS, not in a catalog category, so check the creator's install note if you can't find one in-game.