Whether that’s just marketing BS or real depends on the project. Wether it fits your particular kind of cloud environment is also a different story.
In the specific case of NATS I love how I can start with a single server on localhost, then maybe upgrade to a single fly.io instance, then later move to a larger AWS, instance, then later add some fault-tolerance by turning a single server into a cluster, then later have multiple clusters in various AZs around the world, hosted on different cloud providers.
NATS makes all of these changes (and a lot more) a breeze. Any component or application using pub/sub, KeyVal, durable streams, request/response will just keep working without a single any changes.
Disclaimer: I love NATS, it’s the most promising piece of infrastructure technology I have seen in a long time.