If tuned properly, the clutch will tend to keep the speed at or near the torque peak of the engine. This results in a fair bit of waste heat, but over a broad range of speeds, it is much more useful than a direct drive in many applications.
If tuned correctly, the clutch will maintain the vehicle's speed close to the engine's peak torque. This leads to increased heat generation, but is generally advantageous over direct drive in many situations.