• Finding and correcting design errors
• Learning engineering design principles
• Making products and systems compatible
• Finding patent infringement cases
• Creating documentation when a manufacturer is unwilling or unable to (e.g. no technical data or specs are available on parts, or that information is proprietary, or that information would take a long time to get)
• Reclaiming obsolete products
• Modeling unique or unavailable parts.

Once you've reverse-engineered a system, you can adapt it to new uses, or renovate it, or document its operation, or model it. Sometimes engineers will find a part for which no specs are available, and scan it to create a solid model. Pitfalls to this procedure include

• lack of tolerance specifications
• inability to reproduce original processes
• lack of knowledge of materials or treatments
• lack of knowledge of parts reliability

Copyright and Patent Infringement

Here's how courts might find out whether reverse engineering has led to copyright or patent infringement:

• Identify the unprotected ideas at each step in the reverse engineering process.
• Filter out the non-protectable elements.
  • Sometimes you can only do things one way.
  • Sometimes there's only one most efficient way.
  • Sometimes you have to match standards.
  • Sometimes an idea is in the public domain.
• Once all the above is identified, whatever's left might be protected by a patent or copyright. The courts would compare what's left to the protected original work.

References

van den Brand, M., P. Klint, and C. Verhoef. "Reverse Engineering and System Renovation - An Annotated Bibliography."
Samuelson Law, Technology, and Public Policy Clinic. Chilling Effects Clearinghouse: Reverse Engineering