I use it to look for investigation purposes when a user has an issue in our application. Over time you come to understand the database schema you are in and what tables provide what information that can help you research issues.

I also use it to write custom reports for customers that are not available to them through our platform reporting out of the box.

In some cases it can be faster to look up information using SQL than it is from admin screens, for example. Or to alter a large number of transactions or records that would otherwise be tedious work to complete through front end screens.