The LAMBDA function (currently in beta) lets you define your own re-usable custom functions.
The function syntax to use in your formulas is:
=LAMBDA([parameter1, parameter2, …,] calculation)
|A value that you want to pass to the function, such as a cell reference, string or number. You can enter up to 253 parameters. This argument is optional.
|The formula you want to execute and return as the result of the function. It must be the last argument and it must return a result. This argument is required.
This has the potential to save a lot of time (and increase robustness) wherever you have similar formulas that are not quite the same each time.
One of the big benefits of this function is you can use it to nest different custom functions together.
It will all make more sense as you test out the function and see what it can do in real examples that you actually use.
Will it collapse if you observe it?
No. This function looks so good that it seems to defy physics!
For more information on how to use LAMBDA, see the help docs.
For more background and philosophy on the power of LAMBDA, along with some examples, see LAMBDA: The ultimate Excel worksheet function.