Why is the $sort variable needed?

I do not understand why the $sort array needs to be created. Is that not a duplicate step? I thought one could directly create the $output array with values instead of keys, like this:

if (strtolower($category) == strtolower($item["category"])){ $output[$id] = $item["title"]; } } asort ($output); return array_keys($output);

It works for me like this. Is it bad practice to do?