Rollers are great for working on your cycling form and developing a smooth, powerful, and consistent pedal stroke. If you pedal squares, or jerky, inconsistent strokes, you'll bounce on rollers like a rubber ball—creating a natural feedback mechanism that helps you subconsciously pedal more smoothly.
On average, rollers are more affordable than indoor trainers. Generally, they’re about the price of a good, but pretty bare-bones trainer. That’s partly because basic technology of rollers hasn’t changed much in decades.