It obviously depends upon the context. But for many industrial processes and designs, the design and documentation alone is only the bare minimum needed to replicate it. The rest is in people's heads and hands, and needs to be passed on by training over weeks or months.
Here's a trivial example: in a physical chemistry lab I was working in, I was training a new worker how to do a particular analysis. The ISO 9001 documentation said to pipette 1000µl of the sample and 1000µl of a standard into a 2ml GC sample container, using an electronic pipetter. I got repeated accuracy to within 5 decimal places; the trainee got about 1 d.p accuracy, using the same equipment and samples. Because skill and technique matter, take time to learn and master, and those aren't in the instructions.
This applies to any process. Having the instructions aren't enough. No matter how many designs you rip off, you still need the right people with the right equipment and the right skills and techniques to fabricate it correctly, or duplicate the process exactly, etc. Industrial espionage can only take you so far. The effort required to rip off the designs and documentation might be more than the effort required to do your own design and establish your own processes. Particularly when you're otherwise inheriting other peoples design choices and you need to completely reverse engineer their thinking. In a way, it's similar to how writing software from scratch can be quicker than making a change to a huge legacy codebase. You're free of the design constraints, and you don't need waste weeks ploughing through someone else's mess to find our what those constraints are.
Another problem is the starting materials. Have a read up on the effort required to manufacture FOGBANK, a material used in nuclear warheads. The materials and process were completely documented, but the people who made it were long retired. It took over half a decade of effort to rediscover and replicate the process, not only to learn the techniques but also to discover that the process relied on an impurity in one of the materials which wasn't documented.
Not just in the heads and hands, but in the available infrastructure and supply chain as well. A classic example: SR-71 airframe documentation would probably have been nearly useless for Soviets, since they didn't have good titanium machining capability at the time (they decided to go with steel for MiG-25 airframe, for example).
Here's a trivial example: in a physical chemistry lab I was working in, I was training a new worker how to do a particular analysis. The ISO 9001 documentation said to pipette 1000µl of the sample and 1000µl of a standard into a 2ml GC sample container, using an electronic pipetter. I got repeated accuracy to within 5 decimal places; the trainee got about 1 d.p accuracy, using the same equipment and samples. Because skill and technique matter, take time to learn and master, and those aren't in the instructions.
This applies to any process. Having the instructions aren't enough. No matter how many designs you rip off, you still need the right people with the right equipment and the right skills and techniques to fabricate it correctly, or duplicate the process exactly, etc. Industrial espionage can only take you so far. The effort required to rip off the designs and documentation might be more than the effort required to do your own design and establish your own processes. Particularly when you're otherwise inheriting other peoples design choices and you need to completely reverse engineer their thinking. In a way, it's similar to how writing software from scratch can be quicker than making a change to a huge legacy codebase. You're free of the design constraints, and you don't need waste weeks ploughing through someone else's mess to find our what those constraints are.
Another problem is the starting materials. Have a read up on the effort required to manufacture FOGBANK, a material used in nuclear warheads. The materials and process were completely documented, but the people who made it were long retired. It took over half a decade of effort to rediscover and replicate the process, not only to learn the techniques but also to discover that the process relied on an impurity in one of the materials which wasn't documented.