I was recently sent a file which had the interesting warning message Too many different cell formats. I had not seen this message before and upon doing some research found it was common problem. The message is annoying as after you click OK it does not allow you to add additional formatting even if that is a used format within the file. The solution was rather complex however effective, I found some code which looked to do the job and cleaned it up to the point where I was happy with it.
The solution is robust and does a nice job. I have expanded upon it and have a nice concise bit of code.
The following is the code to achieve the task. It can take a while depending on the sheets you have in the workbook.
Dim obj As Style
Dim rng As Range
Dim wb As Workbook
Dim sh As Worksheet
Dim str As String
Dim aKey As Variant
Dim i As Long
Dim dict As New Scripting.Dictionary
' Tools / References / Microsoft Scripting Runtime
MsgBox "Start # of styles : " & wb.Styles.Count ' Start sytles in wb
For Each obj In wb.Styles
str = obj.NameLocal
i = i + 1
Call dict.Add(str, 0)
For Each sh In Sheets
If sh.Visible Then
For Each rng In sh.UsedRange.Cells
str = rng.Style
dict.Item(str) = dict.Item(str) + 1
On Error Resume Next 'Cover for delete error
For Each aKey In dict.Keys
If dict.Item(aKey) = 0 Then
Call wb.Styles(aKey).Delete 'not used
If Err.Number <> 0 Then Err.Clear
MsgBox "End # of style : " & wb.Styles.Count ' End sytles in wb
Paste into a normal module and it should do the trick. It may take a while to run depending on how many styles are in your workbook.