I have a 6MB Excel 2010 workbook containing several interrelated sheets and charts. None of the calculations are very complicated. The file was getting slow to load so I was looking for ways to reduce size. After making a copy of the workbook I started by deleting one simple column in one sheet (the column computed the diff between two other columns). I saved the file and was startled to see that the file size was now 400K. I've looked through the workbook and all the data (except the one column I deleted) appears to be there. What the heck happened? Can I trust the newly saved file to be complete?