What are product labels and why are they important for Google Shopping?

Simply supplying 1000 products to Google Merchant Center usually leads to a situation where 50-ish products drive most of the sales, 100 products have no sales, but spend 30% of the budget for nothing and the rest is just hanging without either traffic or sales. 

Product labels come in handy by allowing you to easily define product segments with high potential for budget increase as well as those that waste budget. Afterward, the account manager relocates money from the latter to the former thus improving campaign performance.