Why add Excel content to a Word document? To save time and effort in reentering existing text and/or numbers, and to ensure consistency between files. If your Word document discusses numbers already entered into an Excel worksheet, don't create a Word table and re-enter the numbers—copy them from Excel and paste them into the Word document. The result is an instant table, containing the numbers as they appeared in Excel.
Using Excel for tables that contain numeric data also gives you access to Excel's tools for calculation and numeric formatting, which you don't have to the same extent in Word. Therefore, you should try to create, format, and add formulas to the table in Excel—before you copy the table to a Word document.