The woods are getting ready to sleep—they are not yet asleep but they are disrobing and are having all sorts of little bed-time conferences and whisperings and good-nights.

What meaning does the use of personification convey?

It conveys the idea that the trees in the woods are tired and ready for bed.

It conveys the idea of trees losing their leaves and making noises in the wind.

It conveys the idea that the trees in the woods are talking to the author before they go to sleep.

It conveys the idea that the trees in the woods are not able to sleep, so they keep talking to one another.

And for some complementation purpose: Personification (which is the personal nature or human characteristics attribution to a nonhuman living being, or even object) is very useful to 'explain' or just illustrate certain phenomena that could otherwise be too complicated if literally explained.

That's why it's so much used when educating children when they're still too young to understand certain things. Or in fables, which were generally born in times when there were many things in nature not comprehended by human knowledge.