The accounting needs of a business are quite different from that of a person. Businesses have customers that owe money, vendors which are owed money, employee payroll, more complex tax laws, etc. GnuCash offers business oriented features to facilitate these needs.
Accounts Receivable (A/R) are used by businesses to record sales for which they are not immediately paid. Accounts Payable (A/P) record bills that they have received, but might not pay until later. These types of accounts are used primarily when you have a lot of bills and receipts flowing in and out, and do not want to lose track of them just because you do not pay or get paid right away. For most home users, A/R and A/P are too complicated to be worth the effort.