I've tried to use sugar subs 100% in things like cookies, but it never works. The cookies end up very dry and cakelike I figured out that it has to be at least 1/2 to 2/3 regular sugar to sugar sub for cookies to work. It is not impossible, but I've really tried make subs work, but they just don't. I will accept an inferior product for me and my family, but you may not.
For cakes and breads, sugar subs are much, much better and more reliable. I've been able to use 75-100% sugar sub no problem. Applesauce works great for cakes!
Brownies...it depends. Underbaking is always best for these, I've found. Sometimes the result can be rubbery though. I do not recommend skipping oil on these. I tried using prunes for oil and partial sugar sub once and it sucked.
Pudding (American style) also works very well with sugar subs.
Desserts are going to need something to make them sweet and palatable - real or fake.