Use OSI for troubleshooting. Use TCP/IP for implementation.
OSI helps when:
- Debugging layer by layer
- Communicating with engineers
- Understanding function separation
- Studying for certifications
TCP/IP helps when:
- Writing networked apps
- Configuring real systems
- Designing architectures
In interviews, expect OSI questions like "At which layer does a router operate?" In practice, you'll think in TCP/IP terms.