This example demonstrates a number of different applications for null patterns in form objects. This is where a field without a inputted value can display a default message. Note that having the full caption in the value area is not best practice. This is because as soon as the user clicks into the field the null pattern (caption) is cleared and the user may forget what information is required.
Here is a detailed example for null patterns in dropdowns.
In summary, it is a useful technique, but use with caution.