Good question! The answer is... a whole lotta nothin' 😂
In all seriousness though... You do not need an account to checkout with a subscription. You can checkout with a subscription and it will remain active until you change it.
Subscriptions are linked to the email used during checkout.
You only need to register an account if you would like to manage or make changes to your subscription. This can be done at anytime, before or after checkout.
If you would like to manage your subscription, please create an account with the same email you used to checkout. There is more on that here as well.