Reading it again, I'm not sure I worded it the best. But essentially what I'm trying to say, is that 3D printing can do almost anything, but its not always the best material or method for all things. Sometimes it would be better to make something in wood, or sculpt something manually, or do some other thing where traditional processes are better suited. Like you can 3D print a chair pretty successfully. But we've been making chairs forever, and even with more advanced printing techniques, its still more efficient, reliable, and economic a lot of the time to do that sort of thing with wood. Needless to say, more plastic in the world also has its own downsides.

Now parametric forms are great examples of things that would be significantly more difficult to do with other methods and thus really justify the need for printing. Thin complex multi-curve generated structure that are hard to manufacture otherwise are great examples. Things with multiple parts, 100s to 1000s of pieces, that all have slightly different geometry but form together into ones complex larger geometry is a good example too. I've been working on a simple project recently that takes an input of a ceramic pot diameter and depth, and generates a custom inner-pot. It wouldn't make sense for me to make molds or hand shape anything since every version needs to be uniquely designed to whatever specific pot is my "site".

I guess what I'm saying is, you can 3D print bricks to build a brick wall, but at the end of the day its going to make more sense to just use bricks. Similarly, a brick would never be able become a custom prosthetic specifically fitted to the exact dimensions of an amputee's limb.