Around two years back, I posted an article on Continuation Object in Salesforce. As we know because of governor limits like concurrent Apex limit or CPU time limit errors, its always recommended to perform long running Apex process asynchronously. Processes specially like calling external API.
In Short, below are challenges in front of us
We need to call 10+ API from Visualforce
Cannot use chaining of Continuation Object as current chaining limit is 3
We may run into scenario in Salesforce project, where we need call external web service but no need to wait for response. Response from external web service can be processed asynchronously and once processed it can be presented in Visualforce page.