The + is reduntant.
Some people who still use or used Lotus 123 put a + in front of formulas to tell the program that you were entering a formula. Excel uses = instead, but has allowed the use of the + sign, I guess for the sake of attracting the Lotus users so they didn't necessarily have to change this habit.
Try entering a formula like +If(A1="',"","X") and press enter, now go back and look at the formula, you should see =+If...
In Excel, you should really just type =If(......