What is a primary usage of the UNION ALL function in AMC queries?

The correct answer is To unify events from different tables because the primary usage of the UNION ALL function in AMC queries is to combine records from multiple tables into a single result set, without removing duplicates. This is particularly useful when you want to aggregate events from different sources or tables, such as combining data from various advertising campaigns or event types. The UNION ALL function allows you to unify the data from these tables while retaining all rows, providing a complete view of all events, even if there are duplicates. This is different from other functions like grouping or summarizing fields, which focus on organizing or consolidating data within a single table.