User experience is important for a successful E-commerce store.
It may happen that when a customer is redirected to 3rd party payment site, the payment is failed due to some technical error or he decides to postpone the payment process for future, he clicks the back button and gets redirected back to the Magento store with an empty cart. If he wants to place the order again, he has to add products to cart again and proceed from scratch. It hinders the shopping experience.
Such a situation forces the user to again fill the cart which is tedious.
He may decide to abandon the shopping. To avoid it, make sure to restore Magento Quote after payment refusal.
Check https://meetanshi.com/blog/restore-m...yment-refusal/ for the method to restore Magento quote after payment refusal.