Good smart scales also come with apps (some also have desktop interfaces), that help you track you weight over time, among other things. Effortless weight tracking is theri main USP.
Smart scales can also read body-fat or other body-composition (e.g., bone-density) metrics, which helps you get a body-fat percentage estimate.
The best smart scale: Eufy BodySense Smart Scale (easy to use, very great price)
The second best smart scale: Weight Gurus Bluetooth Smart Scale (larger and comfortable platform, goal-focused app, great price)