In September, 2018 we introduced several new functions in a family of functions called dynamic arrays. These functions will automatically populate a range, or array, and eliminate the need for legacy Ctrl+Shift+Enter (CSE) array formulas. Dynamic array aware Excel does have performance implications with regards to how it recognizes legacy CSE formulas.
Whenever you write a formula in dynamic aware Excel, it determines if that formula has the potential to return an array. If it could return an array, we will save it as a dynamic array. You can prevent a formula from being identified as a dynamic array by using the SINGLE function.
If you open a workbook that contains dynamic arrays in an older version of Excel, it will perceive them as legacy CSE arrays.
Following are examples of the MUNIT function entered as a dynamic array, and as a legacy CSE formula. Note that legacy CSE array formulas behave very similarly to dynamic arrays. The major difference is that they are not able to resize, and have no spill border. For a comparison of the two, see: Dynamic array formulas vs. legacy CSE array formulas.
If you know you will be sharing dynamic array enabled workbooks with someone using non-dynamic aware Excel, it’s better to avoid using features that aren't available to them.