Query related to VBA code

Excel 

Sub SplitData()
    Dim d As Object
    Dim ws As Worksheet
    Dim r As Long
    Dim m As Long
    Dim v As Variant
    Dim wt As Worksheet

    Application.ScreenUpdating = False

    Set d = CreateObject(Class:="Scripting.Dictionary")

    Set ws = Worksheets("Main Sheet")
    m = ws.Range("A" & ws.Rows.Count).End(xlUp).Row
    For r = 2 To m
        d(ws.Range("A" & r).Value) = 1
    Next r

    For Each v In d.Keys
        Set wt = Nothing
        On Error Resume Next
        Set wt = Worksheets(v)
        On Error GoTo 0
        If wt Is Nothing Then
            Set wt = Worksheets.Add(After:=Worksheets(Worksheets.Count))
            wt.Name = v
        Else
            wt.UsedRange.Clear
        End If
        ws.UsedRange.AutoFilter Field:=1, Criteria1:=v
        ws.UsedRange.Copy Destination:=wt.Range("A1")
        wt.UsedRange.EntireColumn.AutoFit
    Next v

    ws.UsedRange.AutoFilter

    Application.ScreenUpdating = True
End Sub