1. Deleting a Product & Service
If you delete an item you are still able to create a report.
For example the Comprehensive Report allows you to "Filter" your search by Department, Category or Product & Service.
A suggestion would be if you are going to delete a Product & Service item that you edit the "Name" field and add "Deleted" so that when you are creating the report you clearly see what is active and what is deleted. You could also add the date to the Name for further clarity.
2. Moving a Product & Service item to another category
You are able to move an from 1 category to another.
Example: Moving the Product & Service item "Adjustment" from the chiropractic category to the "Services" category.
Any invoice created prior to the change of category moved the item and history to the new category.