During the design and testing of a table definition, it is often necessary to verify the effect of a change or overall table design. The Preview Table Data form allows you to display table data in a grid so that you can see that the results are what you expected.
You can also use the Query Builder whilst in preview mode to display a subset of the table (based on the columns), and change the ordering. This can be very helpful in detecting and resolving any errors that may have occurred.