In Excel you have the option of entering data directly into a cell or by entering into the formula bar.  It might be easier when initially entering straight data to enter it into the cell.  But the formula bar makes it helpful when entering a formula (equation) or a function.  As you start to enter data, the formula bar will display what you’re entering in the cell along with a Cancel icon, an Enter icon, and the fx icon (which can provide help if you’re entering a function).

When the entry is complete, you can either press the Enter key or click on the checkmark.

However, the cell only displays the result of your formula.  If you want to see how the value was derived you need to look at the formula bar.  Also, if you need to make edits, the formula bar is much easier.  In the following example, the result in the cell indicates a problem.  The formula bar will indicate exactly what was entered.  In this case, the last part of the function should have been 7, not 8.

Once the correction is made, the cell displays the correct result.

You can also use the formula bar to edit formulas or other data located in the active cell by clicking on the data in the formula bar with the cursor.  Then you can modify those ranges.

So the formula bar makes it much easier to work with your formulas, especially when editing them or auditing for errors.