Links give you traceability, which helps you verify that what you are building satisfies your user requirements.
You can follow links in both directions. For example, if a test fails, you can find out which requirements are affected by the failure. You can trace the links from the test back to the design features, and then to the system requirements.
With links, you can also effectively manage change. You can quickly trace the impact of a change to a single piece of data on your system.
For example, the engineering department tells you that they cannot deliver the solar-powered battery you were expecting. You can trace the links from the battery object back to the requirements that depend on it. You can also trace the links forward to the features of the car that depend on having a solar-powered battery. You can quickly see the full impact of not having a solar-powered battery. You can make an informed decision about whether to use a conventional battery, or whether to invest more to deliver a solar-powered battery.