One Page Checkout is a type of checkout in which all information required to perform a transaction displays on a single page divided into logical blocks:
for personal data;
One Page checkout is considered a faster and more robust option, but it may lead to errors during data submission. New customers may be confused by the number of fields to be completed all at once.
This is how One Page checkout type will look for an unregistered customer:
For a logged-in customer, personal data (shipping and billing addresses) displays predefined hence the only necessity is to select the preferred shipping and payment methods.