DIFFERENCE BETWEEN TOOTHED PULLEY AND FLAT BELT PULLEY

1) Flat Belt pulley's  are used inline shafting to transmit power in factories. They were also utilized in infinite farming, mining and work applications, like saw mills, water pumps and electrical generators. Whereas toothed pulleys are usually accustomed transmit direct motion for indexing. They are usually utilized in part of chains of gears. Camshafts of vehicles, miniature timing systems, and stepper motors often utilized these belts. Toothed pulley are called timer pulley also.

2) Flat belt pulley's doesn't have teeth (have no teeth), whereas toothed pulleys have teeth that match into an identical toothed counter.

3) Flat belts tend to slip on the pulley when heavy loads are applied, where as toothed belts haven't any slippage when properly tensioned. 

4) The toothed pulley is employed when correct transmission of the torque is required. A 100% accurate transmission of the torque is not possible by Flat belt pulley's or V-Belt pulley's, as a result of this there is always some (very little) slipping between the pulley and belt.

5) Toothed pulley's are more efficient because timing belts desires least tension of all belts where as flat belts desire more tension compared to toothed pulley.

6) Purchase cost of flat belt is less than toothed pulley.

These are the variations those i know, hope it will be useful to you.