In general, the feature preserves information about customers using a long-term cookie. Once a customer logs in to a site, a long-term cookie is established for that browser/device combination. The customer is now able to view the contents of their shopping cart in subsequent sessions without logging in again.
With persistent shopping cart, a customer can add a product to their shopping cart from one browser session at work, review his shopping cart and change the product configuration from his mobile device and then complete the transaction at home with another computer (session login required initially per browser/device combination to establish the long-term cookie). The persistent behavior feature reduces consumer frustration when they try to access their shopping cart from multiple browser sessions. This feature also enables merchants to provide promotion, according to pre-defined segmentation rules, encouraging consumers to add items to the shopping cart and complete their purchase.
In Magento Enterprise 1.11, persistent shopping capabilities are extended beyond the shopping cart to other features including wish lists, recently ordered items, view and comparison and customer group membership.
Note: The user must log in once per browser/device combination to establish persistent shopping
How does it work?
Magento stores a long-term cookie in each browser (per device) once the customer logs in or creates an account using that browser. The long term cookie allows us to re-create some of the session the user had when they were logged in previously. For example, a users shopping cart is re-created upon subsequent visits to the site. It does not allow the customer or another user to access sensitive information. The user will not be able to complete the checkout process or access account information unless they are officially logged in. Persistent shopping cart is completely configurable by merchants, provides an additional way for the merchant to strengthen customer satisfaction and loyalty and helps increase conversion rates.