Excellent article.

You mentioned not knowing a real world application of the CROSS JOIN.

In my experience, this is typically used for creating test data.

Sometimes you need to test data in all sorts of different configurations. By using a cross join, you can set up the different parameters and try all combinations.

Additionally, if you are trying to create bogus data for a test environment, this is one way of taking data from different parts of the real data and generating new data that is not actually real.

In many cases, this type of join is used on temporary or memory based tables in a batch since the data it produces often needs to go through additional transformation and filtering before it is useful.

I guess, technically, it isn't used in a "real world" application, but it is used for real world issues.