A heating core is used to help the cake bake evenly. Especially when you are using larger pans, the outside of the cake gets done faster than the inside does, so either the edges of the cake are too done, or the center is not done enough. The heating core causes the center of the cake to bake as same as the edges, because the core distributes the heat throughout the cake pan. Hope this helps. Hopefully, I did not thoroughly confuse you.
It is my opinion, that if something doesn't need to be fixed, don't try to fix it. If your cakes are baking fine without the heating core, then you obviously don't need to use one in the size of cakes you are baking. I don't have to use a heating core for my 8 or 9 inch cakes..it is the larger cakes that I use the heating core with..and yes, I just turn a flower nail upside down and pour the batter in..it will leave a small hole in the cake, but it will be covered with frosting.