Not all the time, lots of folks are pre internet and this Myth has been passed down through word of mouth for decades.
Some of the older generation I know wouldn't even think about coming onto a forum or learning anything new so they carry on the way they have done it for decades, because it works for them, But as we know weed is hard not to grow so it "working" or been "optimum" are different things entirely.
Don't get me wrong, I agree, you cant argue with science!
The Myth will die eventually, took a long time for folks to accept the world was not flat though.
@Marcuz516 If your going to do it regardless of the plant science then you will know because the leaves will change colour, the plant will yellow as it takes nutrients no longer available from the medium from the leaves and uses them up to finish. It will starve and fade.