This indicator states that alternative historical data (AHD) from a plant/material combination is only to be deleted if the period indicator is different in the material master.
This situation can arise if, for example, W was entered as the period indicator in the material master for a material and then alternative historical data was loaded. If the period indicator in the material master is now changed to M, for example, the alternative historical data for the period indicator W remains unchanged. If you specifically want to delete such data only, set the indicator. If you do not set the indicator, all alternative historical data for the aforementioned combination is deleted. This can be advisable if you no longer need the data or if you have accidentally loaded the wrong data.