Ooh the 1/3 speed thing is my consultant's hobby horse!
She is of the opinion that regardless of what's in the sauce, you need a third of your plate to be speed as it reduces the portion size. in group she waves her special speed plate round like a maniac. She believes speed is a bonus food if in a sauce.
It's always funny when the vegetarian in our group, who cooks lovely looking vegetable curries, chillies, ratatouilles tells us what she's had and our consultant asks her where the speed it...she's a bit batshit is our consultant.
Personally, I'm all for the common sense approach - if you've bulked out a curry with lots of veg it's just daft piling a load more veg on the side for the sake of it. I just use a smaller plate so I can't put so much on!
For other types of meals, I do tend to stick to it.
Occasionally, I can get too into 'the plan' and it's easy to forget that free food still has a calorific value and speed doesn't magically lose its nutritional value because of where you put it on the plate.
If your weightloss stalls, give it a bash - I do think there is some merit in the portion control function and do find I eat less when doing it.