The wish-list feature allows your customer to browse and save products that they like throughout your Shopify store. 

The users can add those to their wish-list so that they easily find them the next time they visit your shop. This is very useful for them if they want to think about their purchase, wait to receive their paycheck, or simply ask for their friend's opinion on what they like most. 

Being able to easily access this list through their account generates additional sales, makes your customer want to come back more often, but also simply makes their lives easier.