Metadata lets you attach non-variant customer preference or metrics data to a subscription, cart, customer, or shipment, which can then be viewed on the customer’s subscription details page, shipment exports, or via either the Store or Merchant API.
For example, you may want to track the advertising campaign that brought a customer to your site. By adding metadata for the campaign, you could calculate lifetime value of customers correlated to advertising campaigns.
Metadata can be added to a customer’s subscription via either the Store API from JavaScript on the store's website or the Merchant API from an external process.
Metadata should not be used for surveys
In Spring 2016 we added a new survey builder. While metadata still exists and can be added to objects, custom-coded forms that collect information from subscribers is not recommended.
Using Marketplace?
Collecting metadata will not be reflected on your marketplace listing. If you need to collect additional information from your subscribers, you should use the survey builder on the subscription product page.