You are certainly right.  This stuff is great! Heres an example of how you can use it.  We have spreadsheets that are used by Americans and Europeans and wanted them to be divided into an English unit side and a Metric unit side. (The actual calculations can be in the cells on either side.)  It's easy to make the outputs in both English and Metric simply by converting the final calculation outputs cell over to the other unit with function in cells on it's respective side, but we wanted the input to be in either English or Metric with automatic, dynamically updated unit conversion to the other side. There are probably other ways of doing this, but Sheet Event Programming did it seamlessly. Here's an example (The variables in square brackets are named input cells, those that end in an "M" are on the Metric side of the speadsheet.)

Private Sub Worksheet_Change(ByVal Target As Excel.Range)
    Application.ScreenUpdating = False
    On Error GoTo ExitSub
        Select Case Target.Name.Name
            Case Is = "Dia"
                [DiaM] = [Dia] * 2.54
            Case Is = "DiaM"
                [Dia] = [DiaM] / 2.54
            Case Is = "H"
                [HM] = [H] * 2.54
            Case Is = "HM"
                [H] = [HM] / 2.54
            Case Is = "Temp"
                [TempM] = ([Temp] - 32) * (5 / 9)
            Case Is = "TempM"
                [Temp] = ([TempM] * (9 / 5)) + 32
        End Select
ExitSub:
End Sub

Update on using the "Worksheet_Change" event.  Below I have corrected the sample program I submitted earlier.  Note that I have added two lines.  These are necessary to keep the program from initiating itself each time it changes the worksheet. (Without these changes, the program still works, but it runs much longer than it needs to.)

Private Sub Worksheet_Change(ByVal Target As Excel.Range)
'Example Worksheet Event Code to convert between Metric and English units in input cells
'  CAUTION delete the "t" in front of the subroutine name.
    Application.ScreenUpdating = False
    Application.EnableEvents = False'<<<<<CHANGE
    On Error GoTo ExitSub
        Select Case Target.Name.Name
            Case Is = "MdotE"
                [MdotM] = [MdotE] / 2.204623       'lbm/hr >> kg/hr
            Case Is = "MdotM"
                [MdotE] = [MdotM] * 2.204623       'kg/hr >> lbm/hr
            Case Is = "DiaE"
                [DiaM] = [DiaE] * 2.54             'inches >> cm
            Case Is = "DiaM"
                [DiaE] = [DiaM] / 2.54             'cm >> inches
            Case Is = "PressE"
                [PressM] = [PressE] * 6894.757     'psia >> Pascals
            Case Is = "PressM"
                [PressE] = [PressM] / 6894.757     'Pa >> psia
             Case Is = "TempE"
                [TempM] = ([TempE] - 32) * (5 / 9) 'F >> C
            Case Is = "TempM"
                [TempE] = ([TempM] * (9 / 5)) + 32 'C >> F
        End Select
ExitSub:
    Application.EnableEvents = True '<<<<<CHANGE
End Sub