What is the main purpose of Roll-up summary fields?

Roll-up summary fields primarily serve the function of aggregating data from child records and displaying that summarized information on a parent record. This capability allows users to view important metrics without needing to run separate reports or perform manual calculations. For example, in a relationship where a 'Parent' object has multiple 'Child' objects, a roll-up summary field can compute totals, averages, or counts of specified fields from those children.

This feature enhances data visibility and reporting accuracy, making it simpler for users to understand key performance indicators or statistics related to their business processes at a glance. By automating the summarization of related child records, roll-up summary fields save time and reduce the risk of human error associated with manual calculation methods.

The other options pertain to different functionalities within Salesforce. While data validation and executing Apex triggers are important aspects of data integrity and process automation, they do not involve summarizing related records. Similarly, returning API values from external services is a distinct action related to integrations, not the aggregation of child records.