I don't really have a hard and fast rule for how to use them. I've lost eating all of them (blew them all in one sitting at a world famous, 8 course dinner restaurant with a serving of wine with every course--and still lost 2 lbs that week! :O), and lost eating none of them.
I'm in recovery from binge eating (like, serious binge eating), so I plan three nutritious, balanced meals per day plus one snack. So when I use my weeklies, it's generally to round out dinner or have a more dense snack. Or I use them for special occasions (luckily a dinner out like I described is a once every few years occasion, but it doesn't trigger my binging to have a half cup of awesome ice cream from our favorite real ice cream place or to have a small piece of cake at a birthday party, so I do allow myself to have that if I *want* to).
I think each person has to decide what works for them. I know successful folks who eat all their weeklies every week, divvying it up between the days of the week so it's even; other people who are kind of middle of the road like me, and people who don't ever use them except in an emergency. I don't think any of those things are wrong.
I notice that I used them a lot more in the beginning than I do now. For the first month of program I ate all of them religiously every week, but now I don't need or want them as much. I can imagine using them more if I were to train for an athletic event, or if I was losing weight too quickly (I don't want to lose a ton of muscle).