Cheesecakes:

If I make a vanilla cheesecake using sugar and cut it into 12 pcs. Each piece has:
394 calories
28 grams of fat
31 grams of carbs
7 grams of protein.

If I use the same recipe and use Splenda in the filling, but still use sugar in the crust:
335 calories
28 grams of fat
16 grams of carbs
7 grams of protein

Calories is not that big of a difference because so many of them come from fat, but for a diabetic who is "pumping" insulin and has to count grams of carbs or is on the exchange diet and has to count units (15 g of carbs per unit) it's twice as many per piece to use sugar. Probably quite a difference, especially for people who use fast acting insulin.

Plus - if you top it with fresh fruit, it also has carbs to be accounted for, even though it is natural sugar it's still a carb!