Quality requires repeatability and reproducibility. That requires some process to ensure valid results. Flow charts and SIPOCs are tools used to define a process.
The cost associated with quality is dependent on the processes to design quality in, or to remove errors detected, so if you want to estimate the cost of the process, you need to clearly define the process itself. Saving Changes...
To add to Keith's feedback, a flow chart can show key steps in a process where failures could occur which could be prevented (ideally) or corrected. A SIPOC can show the key internal and external relationships as well as the key inputs to a process which could all be points of failure.
Both can help in assessing the complexity and fragility of a process which would directly relate to the COQ.
