Why do we need chaining of Continuation Object ?

From Apex, we can only chain 3 Continuation Object
If we call API synchronously, chances are very high that it will run for more than 5 sec and contributing towards Concurrent Apex limit
Getting CPU timelimit error is also high
Making synchronous call also means risking scalability of Salesforce instance
You don’t want user to wait till call out completed, let them work and update user interface once response is received