Cake kits are usually used in cakes you purchase from chain store bakeries (other bakeries utilize them as well). I usually like to create my own cakes or use the Wilton character pans for character cakes, but I have done some cakes using the kits.
Disney Princesses can be a joy for any little girl to see on her birthday cake, but it would be difficult to put more than one on a small cake without cake kits. The kits can often be purchased at the chain store bakery or online (I like buying them at Amazon). Also, if you need to spray the background, Wilton's has a wonderful easy-to-use spray can (Color Mist Food Color Spray) that can be purchased from Wilton's (Color Mist) or from most craft supply stores (I use my local A.C. Moore).
For the My Little Pony: Friendship is Magic cake, I added Pinkie Pie and Spike, as well as cupcake rings. The great thing about this kit is that the two figures (Applejack and Twilight Sparkle) were the same size as the molded plastic toys, so they are a great gift to any MLP fan.
Barbie! No series of cakes can be complete without Barbie. This cake design required stacking the cake, and removing a section of the top layer (for Barbie's patio). The "dream house" opens in the back, is decorated inside, and comes with paper doll cut outs to play with.
I consider the My Little Pony: Friendship is Magic and Barbie cake kits to be super kits. They truly are usable toys that you decorate cakes with.
I hope that these designs might inspire others to try at home decorating. I'll be back soon with more cakes!