Accounting Errors related to Cost Management

I am facing the below errors as per the report generated for Receipt Accounting and Cost Accounting. Can you please guide on whey these errors are thrown? While I understand, that these are related to Mapping set not configured, I would like to know as to why these mapping sets are used in the first place.

For example, while performing the setup in the fusion application, I ran all the transactions in the system, generated the cost and receipt distributions and based on that I had configured the necessary mapping sets. However, once the application went live I see many such errors are coming up wherein I had not configured these mapping sets. I would like to understand on how to debug and understand which mapping sets are referring for what kind of transactions in both Cost and Receipt Accounting.