I often use dependent dropdowns to automatically fill in supporting fields when a user makes a selection from a list.
For example a user may select a delivery city and the distance to that city will automatically fill in a box below.
I would like to allow the user to have the option of overwriting that delivery distance value for the record being created. I don't want to add this temporary value to the lookup table, I just want this record to to have this unique value when saved.
Another example: User selects a certain model of truck. The fuel mileage fills in below as 15 mpg. But, the user know this truck has a unique situation that will reduce the mileage to 10mpg. I would like the user be able to overwrite the 15 with 10 and save the record.