The purpose of the data validation feature in Excel 2010 is to control what users can enter into a cell and to ensure that the data entered is accurate and consistent. It allows you to restrict data entry to certain cells by using data validation, prompt users to enter valid data when a cell is selected, and display an error message when a user enters invalid data. The feature is useful when you want to share a workbook with others and want to ensure that the data entered is within a certain range of dates or numbers, or that only positive whole numbers are entered. By applying data validation to cells, you can limit user entry to predefined items in a list, restrict entries to certain types of data or values, and calculate the maximum allowed value in a cell based on a value elsewhere in the workbook. The data validation feature also allows you to display a custom message if users try to enter invalid data. Overall, data validation helps to ensure standard data entry and systematic reporting, which is important for accurate data analysis and decision-making.