You can select this option when you have entered an Alternate unit with a Conversion factor other than 1,0 under the General tab. Here you select if you want to show the Planning info in the alternate unit. This will be shown here in the fields under the Planning info heading, in the printouts from the Requirement Calculation and in Purchase Order Suggestion in the Inventory module and in the Print Delivery Schedules and Print EDI Delivery Schedule procedures in the Purchase module
Please note that actual purchase order rows generated from Purchase Order Suggestions, are configured by default in the alternate unit for these parts.