What Compiling Does
What happens when a class is compiled? The Studio Output window gives us some clues.

First, the class definition is processed. If it contains any errors, they are reported during this phase.
Second, the system automatically creates a table definition in the database, making our Film data immediately available via SQL.
Third, the system creates a routine, which is the compiled form of a class definition and one of the “secrets” behind the superb performance delivered by Caché applications.