The reason for not banking activity points, IMO, is that the day that you exercise you burn the most calories, so you should be eating more. If you're banking them for a day when you're not exercising, or if you do, are you burning enough calories for the added load..?
For myself, I generally try to get 4 activity points a day, minus Saturday as that's my day off from normal exercise. I strive to only use 4 extra points that day. I try not to use my 35pts at all. If I do, I do.. but I try not to. What I have been trying to do is only have 1 day a week where I "splurge" a bit and enjoy the day.
I find that when I use my activity points the day I get them, I lose more weight. See when you exercise your metabolism burns faster for 24hrs. That's why exercising is great in the morning. It is a metabolism boost for the whole day!
That being said: Everyone's body is different. Some people can't use the 35 pts OR activity points or else they don't lose anything. Some people can use everything and lose. Some people, like me, find a happy medium. It takes some time to figure out your own body. And, once you find what works for yourself points wise, stick to it and don't let anyone tell you different. You know your body, you know what works.
I.E. I generally, unless I'm having 2 servings of fruit at once, don't count fruit as points. I know you're supposed to. But, to me, fruit is healthier than a piece of chocolate, I'm going to reward myself! And that works for me. I haven't noticed a weight increase of any sort because of it. But, not everyone's body can do that.
Find your balance and enjoy the journey