You are limited in the number of calories for sweet treats (It's 100 now right?). And I think the purpose of that is to limit consumption of artificial sweetener. Of course, you could drink splenda-sweetened drinks all day and never hit the limit, so there is a way around it. I don't think splenda intake has specifically been limited. Generally, though, I don't think it's good to use too much. I try to limit to one or two packets/day. It does seem to cause cravings in some people, and it gives me gas if used in excess.
There is like under 1 gram of carbs in 1 splenda packet and it says 0 cals... but obviously is has to have some calories in more amounts.. I use splenda in my water (with a squeeze of lemon) and my iced tea and coffee.. I LOVE IT.. I think its better than sugar itself!
I say, if its not causing you cravings and what not go for it.
If I remember correctly, the Splenda that measures the same as sugar (in the big bag), is 50 calories for a cup. I count it in when I am using recipes but often I'm not suing very much at a time.
I use 2 packets daily in my cereal, sometimes 1 or 2 in my Greek yogurt. And I drink a lot of diet pop daily, plus an occasional skinny latte. So I guess I use a lot. It doesn't cause any problems for me and helps me enjoy my food.