Complex calculations can produce values with a large number of decimal places. However, most people will rarely need to work with such numbers. Whether finances, percentages or measurements: after two decimal places, the digits are usually less important. Numbers with many decimal places can look messy. Therefore, it’s important to prune back the number of decimal places to a useful length, i.e. round them down.
There are numerous ways to do this in Excel. For example, many users are familiar with the option to format cells so that only a predefined number of decimal places will appear in the result cell. However, this only adjusts how the value is displayed. The original number still exists in the background in Excel. This can have its advantages: if the value is used for additional calculations, the full correct number will be used. On the other hand, this is not always what you want. If you want to adjust the actual value, you will need to do so with a function like ROUNDDOWN which allows you to adjust a number to your preferred number of decimal places.