XLOOKUP can handle arrays natively, which makes it a very useful function when constructing criteria based on multiple logical expressions.
When this expression is evaluated, we first get two arrays of TRUE FALSE values like this:
When the two arrays are multiplied by one another, the math operation results in a single array of 1's and 0's like this:
We now have the following formula, and you can see why we are using 1 for the lookup value:
XLOOKUP matches the 1 in 8th position, and returns the correponding 8th value from B5:B14, which is 0347.
With a single criteria
As seen above, math operations automatically coerce TRUE and FALSE values to 1's and 0's. Therefore, when using multiple expressions, a lookup value of 1 makes sense. In cases where you have only a single criteria, say, "amount > 250", you can look for TRUE instead like this:
Alternatively, you can force the TRUE FALSE values to 1's and 0's, and use 1 like this.