How to detect amount of changes in cell?

Perhaps storing as a Name would be best, then it should be less likely to be deleted accidentally

Option Explicit

Private Sub Worksheet_Change(ByVal Target As Range)
    Dim CellChanges As Long
    If Target.Address = "$A$1" Then
        On Error Resume Next
        CellChanges = Evaluate(ThisWorkbook.Names("USED").RefersTo)
        If CellChanges < 1 Then CellChanges = 1      'first used
        CellChanges = Evaluate(ThisWorkbook.Names("USED").RefersTo) + 1
        MsgBox CellChanges    '<- test delete
        ThisWorkbook.Names.Add Name:="USED", RefersTo:="=" & CellChanges
    End If
    On Error GoTo 0
End Sub