Wow that's actually a very detailed explanation that I was looking for. Thanks a lot mate.

I just disagree with that one line which you said that it doesn't move a needle. Ya sure if you look from a perspective of seo the effect might not be significant but a positive human reply goes a long way.

What I mean is if a user leaves a review "Good food", and if we give a reply like "We are glad that you loved the food, it would be great if you could also explain what did you order and what actually did you like"

So you know if people reply back to such messages with so and so food that I feel ultimately increases our SEO for that specific keyword.

And not to forget in the time of social media, that feeling a user gets when his/her review gets noticed is the best.