When would you use an annuity factor in a net present value calculation instead of a present

Question:

When would you use an factor in a calculation instead of a present value factor for a single cash flow?

Net Present Value
What is NPV? The net present value is an important tool for capital budgeting decision to assess that an investment in a project is worthwhile or not? The net present value of a project is calculated before taking up the investment decision at... Annuity
An annuity is a series of equal payment made at equal intervals during a period of time. In other words annuity is a contract between insurer and insurance company in which insurer make a lump-sum payment or a series of payment and, in return,...