When setting up an import definition in a DEV model you set it as production if you need the admin in the PROD (deployed) model to change the definition of the import.
This is rare, as normally you shouldn't need to re-define the import action settings in PROD alone.
More often the Import Source might change (e.g. coming from a different saved view), so setting the source as production is common.
Remember, if your model is in Deployed mode, don't take it out of Deployed mode. IF you get an error if/when you try and amend the import, you will need to make the change in DEV. Either make the change to the import and sync, OR, set the import to production and sync.