When you type something in a cell after an = sign in Excel, a list of functions is shown. Functions have an icon next to them. For some functions, the icon shows a Yellow triangle with an exclamation mark. That is the Excel Function Warning I am talking about.
No warning 
Warning 
What exactly is the Excel Function Warning?
It basically means: “Do not use this function. We have a new and more accurate function available now”. If you use only newer versions of Excel, you should use the newer functions.
Standard Deviation
Here is an example. The older STDEV function now has two separate functions STDEV.S and STDEV.P – S means sample and P means population. The mathematical formula used behind the scenes by these functions is different. As mathematics advances further, the logic used also undergoes improvement. The newer functions utilize the latest algorithms to increase accuracy of your results.
Best practice
- Notice if any of the your formulas have one or more Excel Function Warning icon.
- Go to the help file of that function.
- The newer, better or more appropriate function will be listed there.
- Learn the new function(s). Understand what has changed and why.
- Change these across your files to ensure more accurate results.
- Use the new function when you create new workbooks.
