As of 2020 or 2021, Excel has lambdas!
This can save you from repeating yourself or using intermediate cells.
For example, when you have an array formula, Excel, quite annoyingly, coerces blank cells to zero instead of the empty string.
Before, to work around this, you would have had to say =if(isblank(...longformula...); ""; ...samelongformula...), but now instead of repeating yourself, you can go =lambda(x, if(isblank(x); ""; x))(...longformula...)
@clacke LET does the same job and reads a little more plainly: =LET(v; ...longformula...; IF(ISBLANK(v); ""; v))
Microsoft's own note on LET is the bonus: an expression written twice is calculated twice, and a named one once. So the old IF(ISBLANK(long); ""; long) pattern was also paying for the long formula twice.