The problem is that you have to run the code in your head to understand what it means. It obfuscates the intent. Just read it aloud and you'll see what I mean,

"Once upon a time there was a variable named, totals that was initialized to an empty array. Next, a for loop happened and some var, i appeared (his name doesn't really matter.) i was initialized to 0. Enter stage right, totals's buddy, orders. orders has a property named length. i was told that it shall be incremented by 1 so long as i was less than order's length property. Sadly, the for loop was just using i. i didn't know it would be disregarded once for loop was finished.

Not surprisingly, what happened next was quite remarkable. The total property of orders index i lept onto totals. i was incremented. Then the total property at index i lept onto totals... i was incremented... Finally i was greater than or equal to orders.length, so the for loop ended. totals lived on, changed by its journey while i was never seen or heard from again.

Study guide question: how did totals's character change by the end of the story and what did this mean?" "

The following code snippet means the same thing, but it's also self-documenting. Plus there's less accidental complexity:

    var totals = orders.map(function(order){ 
        return order.total;
    }); 

Read it aloud and you'll see what I mean,

"Once upon a time, there was a var named, totals. It was a list of order totals. Fin."