Was the voiceover an afterthought?

Watching this film (again, it's a habit) I started to listen to Robert J. Steinmiller's words more carefully and imagining what the film would be like without them. I came to the realisation that in fact the voiceover isn't needed, it seems to be a lot of visual narration just to slide in a few facts that an unintelligent viewer might miss.

Don't get me wrong, it's pleasant enough, but if you listen to his words you'll realise that each word either tells you what you can already see he's doing onscreen ('I used to wait for Mrs Sampson to fall asleep, and sneak into his bedroom to watch.') or it points at the theme ('I didn't know yet what I was going to learn that summer, that monsters were real.').

"I don't reckon I got no reason to kill nobody."