What is the advantage of using an if statement instead of just creating a formula?

Example:

Worksheet 1
Cell A11 contains 150
Cell A12 contains 100

Cell A14 contains this formula =If(A11,(A11-A12)/A11,"") which returns .3333333 in cell A14

Worksheet 2
Cell B11 contains 150
Cell B12 contains 100

Cell B14 contains this formula =sum (B11-B12)/B11 which also returns .3333333 in Cell B14

What is the advantage of using the "If" Statement over a regular formula?

Thanks

Rick