A billing profile is a set of billing details such as customer's credit card information and/or billing info (first and last name, company, address, phone, e-mail, etc.) It is required to collect payments from a customer.
One customer can have multiple billing profiles, but only ONE ACTIVE AT A TIME. For instance, a user can have two credit cards, VISA and MASTERCARD, and a check account. This user can have three billing profiles, two for credit cards and one for checks. If the VISA billing profile is set active, the MASTERCARD won't be charged and no check payments will be necessary.
One billing profile can be used for multiple accounts. This means a user with several accounts can pay with one card or receive all bills at one mailing address.
Trial users don't have billing profiles until they choose to become pay users. The system, however, tracks all trial user's purchases and includes them into the first bill.
When edited, the billing profile is not actually modified. Rather, a new version of billing profile is created, and the old version is preserved to allow tracking payments.