As I said, just another tool. And I think it can be useful when comparing similar vehicles or vehicles likely to be driven by similar drivers....it's a reasonable assumption that certain cars that appeal to safety minded and "boring driver" owners will have lower fatality ratings based entirely on driver behavior per registered vehicle as opposed to physical safety measures.
The drivers of a Mercury Grand Marquis are likely to be fair boring. The drivers of VW Passats are likely similarly boring, though probably skew younger. Both cars have very similar NTSB ratings. But one rates 16 deaths per million and the other 83. That's a pretty big disparity. I'm sure there's any number of reasons why, but one car is a design that is decades old, the other is based on much more modern design.