What happens if I delete or deactivate work types or modules?

The general way that Intervals works is if any module or work type has tasks or time that has been accumulated, they cannot be deleted. Deletion isn't very friendly with reporting. If a work type or module has not been used at all, then the Trashcan icon is available and they can be deleted.

What if I don't want to use that item any more?
You can always deactivate an item if you do not want it to be used any longer. Deactivated items still show up in drop downs and will have an * by them. Deactivating is like saying "OK, we don't use this any more, but we need to keep it around for historical information".