HR is a great case in point due to the conflicting advice and occasionally the subsequent hardening of tolerances. In my humble opinion, the human body is far too robust to be corralled in to specific boxes that are good or bad. There's a massive amount of grey rather than the black & white that is mistakenly assumed, and this grey zone will change on a daily basis.
Just to confirm, I think that is what is being said above, so I'm not saying that anyone is wrong, but it's also important to call out the issue as it could become a fool's errand trying to attain the holy grail of zones, only to achieve training regression. I think that has happened to me previously on certain occasions.
Trust your instincts and intuition, it's very often right as long as it's interrogated properly to weed out any mental weakness for just not wanting to endure.
Just my two cents worth
