Some of the workbooks that I use have anywhere between 5-15 spreadsheets, but
when its open only a few of those will actually be used or have any changes
made in them. So... Is there a way to adjust the macro below so that it will
only run in the spreadsheets that had changes made while the workbook was
open?

Private Sub Workbook_BeforeClose(Cancel As Boolean)
Dim wS As Worksheet
Dim c As Range
For Each wS In Worksheets
For Each c In wS.UsedRange
If Not c.HasFormula Then
c.Value = Trim(c.Value)
End If
Next c
Next wS
ThisWorkbook.Save
End Sub