A good stylus makes it easier for you to draw, sketch, doodle, and .write notes. They help you use touchscreen devices in cold weather. A stylus also helps you with accessibility issues that might make touchscreen navigation difficult.
However, do not get a stylus if you only use your touchscreen device to browse and consume content.
The best iPad stylus: Adonit Mark (comfortable and affordable)
The second best iPad stylus: Studio Neat Cosmonaut (rugged body)
The best stylus for iPad Pro users: Apple Pencil (good, pricey)