The advantage of Synchronous Sequential circuits over Asynchronous Sequential circuits is :
Easy to avoid problems due to Hazards
Lower hardware requirement
The transient pulse issues associated with hazards are rarely a problem in synchronous circuits. They are designed to allow sufficient time in each clock period for the glitches of both static and dynamic hazards to resolve. On the other hand, asynchronous logic circuits that can respond instantly to signal changes can be greatly affected. Link
Please make sure it is for asychronous sequential ckt or asynchronous counter.