i do not agree. i train arms with light and heavy days, hitting them twice a week. I have made an enormous amount of progress this way because the "light" day really let's me focus on squeezing the muscle contraction, while the heavy day allows me to be a bit looser with my form
You'd make better gains if you just combined both types in the same workout, and let it recover.
For instance, for my biceps I do
Dumbell curls - 6-8 reps heavy Some body english especially on the last few reps in the last set
Concentration curls - 10 reps - Pretty strict, always squeezing the contraction and a little cheating on the last set to get my 10 reps in.
Hammer curls - 12-15 reps - Just about completely strict and focusing on the squeeze in my Brachs, continuous tension.
You can go heavy and get a little loose with the form and STILL focus on the contraction. Atleast I can...
I have made steroid-like progress with my biceps doing it this way as opposed to twice a week, heavy light days... Without being on steroids of course!