People who use the site search function are looking for a specific product to buy. 

Your site search should be able to match a shopper’s search intent with the product they’re looking to buy. When people search for a product, and find it, they are 6-10 times more likely to convert into paying customers.

Sadly, many eCommerce sites do a poor job of matching shopper intent and shoppers hate searches that return no results - this creates a bad experience for them.