For many of the setup screens, you will be entering items that will be available in drop-down boxes on other screens (order form, client info, etc). Realize that when you make changes to your setup list, it will affect what is available in those drop-downs.
So in the case of your source list, if you have orders entered for a source, you usually should not just delete that source from your list. Instead, mark the source as not being active (uncheck the Active box on the Source setup screen). Then, the source description will still be visible to you on source performance reports, but it just won't be in your active list any longer.
Generally, you want to use a naming scheme with your source descriptions that allows you to keep adding new sources and not remove any of the existing ones, so you can always know which source a job came from.
