In summary, you get snappy, interactive query speeds on large data sets. I've ran that locally and the results are pretty amazing compared to Postgres or even Tableau in-memory.
OmniSci transparently caches data across the memory of the CPUs and GPUs on a server, so after the initial read, it is likely that the data for subsequent queries will be in memory.
We've also optimized our storage formats and multithreaded our disk reads, such that we can easily hit many gigabytes per second on flash storage. Plus, new persistent memory technologies like Intel Optane will enable even more instant reads from "cold" storage.
https://fastdata.io/plasma-engine/
* It's not open-source and I work there.