Clarification on 2007.1 Negative (reduced) Commission

NS folks,

Could you please clarify use of the Negative Commission?  The release notes say:

Now, you can enter negative commission amounts on commission schedules. When creating a commission schedule, you can enter negative amounts or percentages in the commission matrix for the items, classes, departments, or locations you want to pay a reduced commission on.

For example, a commission plan has schedule that pays 10% of sales transaction totals. You can add another commission schedule that pays commission on sales per transaction line item, categorized by item, and enter -5% next to each item you do not want to pay commission on. Then, when a sale is made, the assigned rep earns 10% on the items that are not specifically reduced by the second schedule. The rep earns 5% on the items with the negative commission in the second schedule.