A named one-time-use function has a name that describes what it does. This seems obvious, but bears repeating: instead of having to figure out what a chunk of code does, you can guess from the name and have a series of steps naturally described.
Also, there's more restriction in that the single-use code block only has access to the variables passed into it, which makes it easier to parse, since less things could be happening. It serves to prune variables from the local scope.