To easily spot trends and patterns in your data you can use conditional formatting and visually highlight important values using bars, colors, and icons.  This can be useful and make your spreadsheets look very impressive.  No-one likes to see loads of data and must go through them to find the information they are looking for.  By using conditional formatting, the reader can spot the trends right away.

N.B.  By using the Highlight Cell Rules | Duplicate Values you can highlight the duplicates in your worksheet.  This gives you the opportunity to review the duplicates before they are deleted.