Leave a comment in a formula

This is a tricky use of N() that allows you to use it as a way to leave in-cell comments. It only works for formulas that return numeric results.

The N function takes a value and returns a number. When given a text value, the N function returns zero.

In this case, the primary formula the SUM function, and the N function simply evaluates the comment text and returns zero: 

=SUM(F5:F8)+N("Q4 numbers are estimates")
=SUM(F5:F8) + 0
=410,750

The comment is visible in the formula bar when the cell is selected.