The Subscription Plans field is available in every version of Profile Builder if you have Paid Member Subscriptions plugin activated on your site. You can read more about Paid Member Subscriptions here.
You can use this field to allow users to purchase a subscription plan created with Paid Member Subscriptions through the Profile Builder registration form.
You can specify a field title, description, the plans that should be shown, and also which plan should be selected by default. The plans can also be dragged up and down to change the order in which they are displayed.
This is how the field looks like in the front-end.