There is a big difference between engineered (intelligent) design and evolved (natural) design. Engineered designs tend to become less complex and eliminate redundancies and inefficiencies in function. Evolved designs are unplanned. So they tend to be less efficient and messier. Animal bodies can contain vestigial organs, which have little or no bearing on the survival of the organism but are holdovers from ancestors in which they had a useful function.
A good example of an inefficiency in an evolved biological design is the lack of bilateral symmetry in the two
recurrent laryngeal nerves (RLN) that supply sensation and energy to each side of the larynx in a wide variety of animals, including our species of evolved ape. They are always of unequal length, because the one on the left is trapped underneath the aortic arch, but the right one is free to move higher in a body as, for example, the neck becomes longer over generations. The left RLN has to grow longer as the neck stretches, so giraffes have an extremely long left RLN and a much shorter right RLN. If intelligent designers saw this kind of thing happening, they would redesign the body to elevate the left RLN above the aortic arch, because the extra length serves no function.
Richard Dawkins has written extensively on the difference between biological evolutionary and artificial engineered designs, and that is why he entitled one of his books
The Blind Watchmaker. That is, the watchmaker can still design and make watches, but he just doesn't see flaws in his designs. He may take longer to get the watch to work right or repair its function, and the results won't be as good because of that limitation. Nature's breeding program relies on survival of the fittest in a given environmental niche, but it does not eliminate all of the flaws, or evolutionary detritus, left over from ancestral bodies that it left behind. In order to "see" those flaws, it needs some way to distinguish the necessary parts in the design from the unnecessary parts.