Within Toad, you can optimize SQL that has been identified as an issue. This is a self-contained functionality and nothing is required by the respective database vendors (Oracle, MS SQL Server). SQL Optimizer generates semantically equivalent alternatives with unique execution plans for your original SQL statement and then executes the alternatives to test each statement's performance. This will provide you with execution times and runtime statistics that allow you to find the best SQL statement for your database environment.
If you have used this feature within Toad, you may be most familiar with the use case of being reactive; i.e., a SQL statement is currently running and taking a very long time. Or, you are developing SQL for the first time and want to see if it is optimal. These are the viable use cases for optimizing SQL that are most widely known.
Once this scan is run, a report is produced which will categorize your imbedded SQL statements as Complex and/or Problematic, as seen below. While these SQL statements may not necessarily need to be optimized, they certainly present an opportunity for further investigation on a finite set of statements.
Only by sending them to be optimized will you be able to see if they can be improved.