From a high-level many applications have three main components.
1. They collect data
2. They apply business rules to that data
3. They produce an output
Think of Uber. Uber collects information about you and your destination. Uber then applies business rules to make sure that information is correct. As a final step Uber creates a connection with an Uber driver to fulfill your request. The connection to the Uber driver is the output.
When an application is designed with this paradigm it keeps the components focused. Regardless of how well the interface collects the data, being able to apply the business rules will determine if the data is ready to create the output. You end up with a clearly defined set of business rules to determine the quality of the data.
When the application is built, these components get blurred. It makes sense to bring some of the business rules into the interface to create a better user experience. Having the components conceptually separated makes this a much easier process. The business rules are still applied after the interface. This allows data to come from other sources such as an import feature.
This conceptualizing of the high-level components will make your life as a business analyst easier as it provides structure to how you capture the requirements.