If you have a formula in a worksheet, and the cell referenced by the formula is blank, then the formula still returns a zero value. For instance, if you have the formula =A3, then the formula returns the contents of cell A3, unless cell A3 is blank. In that case, the formula returns a value of zero.

This seems to be related to the idea that it is impossible for a formula to return a blank value, when "blank" is used synonymously with "empty." You can, however, expand your formula a bit so that it returns an empty string. Instead of using =A3 as your formula, you would use the following:

=IF(ISBLANK(A3),"",A3)

This formula uses ISBLANK, which returns either True or False, depending on whether the referenced cell (A3) is blank or not. The IF function then returns an empty string ("") if A3 is blank, or it uses the value in A3 if A3 is not blank.

Regardless of what the formula returns, you can still use its result in other formulas, and it will work fine. Even if it returns an empty string, it is still treated by other formulas as if it contained zero. In areas where treating the cell as if it contained zero might be problematic (such as when you are charting the results of the formula), then you can modify the formula a bit, as shown here:

=IF(ISBLANK(A3),NA(),A3)

This formula returns the #N/A error if A3 is blank. This error propagates through other formulas that reference the formula, but the #N/A error is ignored completely when charting.

While the above solutions are satisfactory for most people, some people would really like to see a target cell be truly blank if the source cell is blank. For instance, you might want cell B7 to be blank if cell A3 is blank. If you put a formula in cell B7 (as already discussed), then cell B7 is not truly blank—it contains a formula.

If this is your goal—true "blankness"—then you can only achieve it through the use of a macro. The macro will need to check to see if the source cell was changed. If it was, then whatever is in the source needs to be copied to the target cell.

Private Sub Worksheet_Change(ByVal Target As Excel.Range)
    Dim rMonitor As Range
    Dim rTarget As Range

    Set rMonitor = Range("A3")
    Set rTarget = Range("B7")

    If Not Intersect(Target, rMonitor) Is Nothing Then
        rMonitor.Copy rTarget
    End If

    Set rMonitor = Nothing
    Set rTarget = Nothing
End Sub