When would you use the PV of annuity table instead of the PV of $ 1 table?

Question:

When would you use the PV of table instead of the PV of $ 1 table?

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,...