This post is the answer to a question in the comments of one of my earlier posts:
Follow the link if you want more info on the drop property.

Miguel asks what the difference is between “Detail” and “All” as a value for the drop property. An example will show the difference.

In this example I have this very simple query that selects from the ClassicModels sample database:

from   offices o,
       employees e
where  o.officecode = e.officecode
order  by o.officecode,

This is what the report layout looks like:

Notice the grouping on the CITY field and that the field appears in the header as well as in the footer row.

Now when I select the cell in the header row that has the CITY field in it, and choose “Detail” as the value for the drop property, this is the result:

And when I choose “All”:

So the difference is in the footer row. Drop All removes all occurrences of the CITY field beneath the header row, while Drop Detail only hides the CITY field in the detail section and still shows it in the footer row.