As Chattiesmom said above, there is some research that shows some behavioral changes due to altering dogs. I have not read it and honestly don't know much about it...maybe I will ask Pstinard about this.
I found this link which is interesting. Even with this, though, there is no way I would leave a pup intact. I have seen too many die due to health issues related to not being altered.
https://www.psychologytoday.com/blog...ed-or-neutered