There are good arguments both ways
On balance I feel having a 'sandbox' is constructive and - if handled right - more welcoming than encouraging people to jump in the deep end
standards in the NN section are lower, visibly so, and the tone of feedback is completely different. I for one have frequently gone out of my way to recognise and encourage contributors to the NN section ... at times I've gone out of my way to read and comment on the NN section when I've completely ignored the other sections.
Having them mixed in with the experienced contributors makes it more likely they get treated the way we address those senior bros who should know better ... and on this forum the gloves frequently come off ...
that's just the way it is and saying "yes but we can see who's a newbie by the number of posts" assumes that everyone who's in a hurry to make a comment before moving onto the next post is going to pay the same thorough attention to detail to make sure their response is appropriate. And that doesn't happen much at the best of times, we all get a bit hasty sometimes!!