Public Sub DropUnusedStyles()

Dim styleObj As Style
Dim rngCell As Range
Dim wb As Workbook
Dim wsh As Worksheet
Dim str As String
Dim iStyleCount As Long
Dim dict As New Scripting.Dictionary ' <- from Tools / References... / "Microsoft Scripting Runtime"

' wb := workbook of interest. Choose one of the following
' Set wb = ThisWorkbook ' choose this module's workbook
Set wb = ActiveWorkbook ' the active workbook in excel
Debug.Print "BEGINNING # of styles in workbook: " & wb.Styles.Count
MsgBox "BEGINNING # of styles in workbook: " & wb.Styles.Count

' dict := list of styles
For Each styleObj In wb.Styles
str = styleObj.NameLocal
iStyleCount = iStyleCount + 1
Call dict.Add(str, 0) ' First time: adds keys
Next styleObj
Debug.Print " dictionary now has " & dict.Count & " entries."
' Status, dictionary has styles (key) which are known to workbook
' Traverse each visible worksheet and increment count each style occurrence
For Each wsh In wb.Worksheets
If wsh.Visible Then
For Each rngCell In wsh.UsedRange.Cells
str = rngCell.Style
dict.Item(str) = dict.Item(str) + 1 ' This time: counts occurrences
Next rngCell
End If
Next wsh
' Status, dictionary styles (key) has cell occurrence count (item)
' Try to delete unused styles
Dim aKey As Variant
On Error Resume Next ' wb.Styles(aKey).Delete may throw error

For Each aKey In dict.Keys

' display count & stylename
' e.g. "24 Normal"
Debug.Print dict.Item(aKey) & vbTab & aKey

If dict.Item(aKey) = 0 Then
' Occurrence count (Item) indicates this style is not used
Call wb.Styles(aKey).Delete
If Err.Number <> 0 Then
Debug.Print vbTab & "^-- failed to delete"
End If
Call dict.Remove(aKey)
End If

Next aKey

Debug.Print "ENDING # of style in workbook: " & wb.Styles.Count
MsgBox "ENDING # of style in workbook: " & wb.Styles.Count

End Sub