Ripple counters are useful in real life. Frequency dividers are an obvious one.
A 16 stage ripple counter will use 1 + 1/2 + 1/4 + ... ~=2 units of power.
A synchronous counter would use 16 units of power.
Generally, synchronous logic solves one set of problems at the expense of
- more Power
- more gates
- lower speed
- new race conditions introduced by synch
- increased emi from continuous clocking and spectrally narrow transitions
A better question might be why do people think synchronous counters are so especially useful? Why is synchronising the entire counter/system seen as the correct solution to the timing of some critical outputs?
Philosophically, the orthodoxy of synchronous logic may have resulted in limited skill and techniques and strategies for making complex unclocked logic systems work, and explain why there are so few asynchronous clockless cpus, even for very simple instruction sets. The Greenarrays F18 is the only one that springs to mind, but able to achieve PIC like power consumption at hundreds of MHz