What are the uses for Cross Join?

If you have a "grid" that you want to populate completely, like size and color information for a particular article of clothing:

select     size,    colorfrom    sizes CROSS JOIN colors

Maybe you want a table that contains a row for every minute in the day, and you want to use it to verify that a procedure has executed each minute, so you might cross three tables:

select    hour,    minutefrom    hours CROSS JOIN minutes

Or you have a set of standard report specs that you want to apply to every month in the year:

select    specId,    monthfrom    reports CROSS JOIN months

The problem with maintaining these as views is that in most cases, you don't want a complete product, particularly with respect to clothes. You can add MINUS logic to the query to remove certain combinations that you don't carry, but you might find it easier to populate a table some other way and not use a Cartesian product.

Also, you might end up trying the cross join on tables that have perhaps a few more rows than you thought, or perhaps your WHERE clause was partially or completely missing. In that case, your DBA will notify you promptly of the omission. Usually he or she will not be happy.

Generate data for testing.

You're typically not going to want a full Cartesian product for most database queries. The whole power of relational databases is that you can apply whatever restrictions you might be interested in to allow you to avoid pulling unnecessary rows from the db.

I suppose one contrived example where you might want that is if you have a table of employees and a table of jobs that need doing and want to see all possible assignments of one employee to one job.