The display setting in Studio's element (or feed) properties page allows you to exclude content in your feed from being sent to the creative upon impression, which is useful for decreasing the data payload of the ad. Any dynamic element that is used by the creative assets must have the display setting switched to ON 
By default, the display setting is set to ON for all columns. If you toggle the switch to OFF 
If you select a targeting data type for a certain column (e.g. placement ID, geographic type, etc.), the display setting toggles to OFF automatically, but you can switch it back if needed.
It's best to leave the unique ID and reporting label columns of your feed set to ON to make it easier to troubleshoot issues. If you switch the display of these columns to OFF, then the values are not included in the payload and are not available for troubleshooting.