When can a validation rule be used to prevent invalid data?

A validation rule is a powerful tool in Salesforce that is designed to enforce data integrity by preventing the saving of invalid data in records. The primary function of a validation rule is to evaluate the values entered into a record during editing or creation. When a record is edited by a user, the validation rule checks specific criteria defined by the administrator. If the data entered does not meet the specified conditions, the validation rule will prevent the user from saving the record, thereby ensuring that only valid data is recorded.

This capability is crucial in maintaining clean and accurate data, as it allows businesses to set strict parameters around what constitutes acceptable data entries based on their operational requirements.

In contrast, when records are deleted, validation rules do not come into play since the records are not being evaluated for data integrity at that stage. Similarly, when records are submitted using web-to-lead or imported, different mechanisms like lead assignment rules or data import validation checks may apply, but they do not utilize the direct functionality of validation rules in the same context as user edits.