Hi Matt,
Great question!
Each of our ticketing plugins actually integrate with a leading WordPress ecommerce plugin (you can choose from Easy Digital Downloads, WooCommerce, Shopp or WP E-Commerce) and it is the ecommerce plugin which handles the checkout experience.
All are capable of letting users login and reuse their details, rather than forcing them to continually re-enter the same information, but for a better sense of how that specific aspect works it would be best to consult the docs for the ecommerce plugin you are most interested in using.
Though it specifically relates to WooCommerce Tickets, this getting started guide will give you a good sense of how it all pieces together on our end 🙂
I hope that helps!