What are the uses of debugs log in Salesforce?

Use debug logs to track events that occur in your org. Debug logs are generated when you have active user-based trace flags, when you run Apex tests, and when executed code or API requests include debugging parameters or headers.
A debug log can record database operations, system processes, and errors that occur when executing a transaction or running unit tests. Debug logs can contain information about:
Database changes
HTTP callouts
Apex errors
Resources used by Apex
Automated workflow processes, such as:
Workflow rules
Assignment rules
Approval processes
Validation rules