What about a lyrics such as "the heart flew away." In a way, it is personification, in another way it is not because people don't fly. But hearts don't fly either. So is it a metaphor then?
I think that the function of personification in songs is to help words come alive. Every time we read or hear lyrics like these, an image conjures up in our head. It's difficult to relay feelings through basic words and in songs, there isn't a lot of room for words. So things have to be expressed as effectively as possible in a short and sweet way. So this is where personification and metaphors come in.