I actually think the advice is more necessary for newbies. First time I did Atkins, I ended up with serious electrolyte issues. I think my body just wasn't properly adapted. Later, eating pretty much the same way, I wouldn't get the issues. I've sort of seen the same thing watching friends doing successive water fasts on line. Weight loss was less dramatic the second and third times around, most likely due to reduced water loss, and maybe reduced potassium and sodium loss to go with it. I do try to get extra sodium and potassium in, but I can't really say that I've noticed anything horrible happening when I don't.

It's a YRMV thing. Stephen Phinney swears salt is necessary for exercise performance, Tim Noakes says salt and water to appetite.