Customers do not need to be logged in to place a recurring order. However, a customer must have a Shopify account to manage their subscription post purchase.
This setting is found in the Recurring Orders admin under Settings > General.
You can either choose to require Shopify accounts - meaning they will not be able to checkout until they register or login with a Shopify account. This adds an additional step to the checkout process.
Requiring Shopify accounts tends to have lower conversion rates than the alternative, but it will depend on the merchant's personal preference.
Or, you can choose to leave Shopify accounts optional. This means a customer can checkout through the Recurring Orders checkout without creating a Shopify account beforehand.
Their subscription will be tied to the email address they typed in during the Recurring Orders checkout process, and they can make a Shopify account (using that specific email address) at any time.
It's easy for subscribers to create a Shopify account post-purchase, but this article will explain how you can make it even easier for them - and explain our use of the Shopify account system in more detail.