The input for "Cost of items for personal use" is there as a reminder to ask taxpayers if they used any of their business purchases for personal use so those amounts can be removed from cost of goods sold, Schedule C, page 2, line 36 which says "Purchases less cost of items withdrawn for personal use".

The two entries of purchases and cost of items for personal use are merely netted together before carrying to the Schedule C. The personal use items aren't actually disclosed to the IRS anywhere. They are just removed from the computation as they are not valid business related purchases.