When to use SIPOC technique

As SIPOC process mapping is easy to use and very scalable, it is often use at the beginning of Six Sigma initiatives when the team want to understand the high level overview of processes that is within the scope of the initiatives. 

The key concept behind the SIPOC is that a particular process should ultimately provide certain outputs/ services to the customers directly or indirectly (could be internal or external customers). If it does not do so, the usefulness of the process is questionable.

Similarly, a process would directly or indirectly requires inputs from Suppliers or Enablers for the process to be performed. By understanding the sources of the inputs, the potential issues of the process can be traced back to the root cause (source).