The point is that you don't need to read in the whole file before you can start working with the data. This is great because it saves you memory (don't need to

The point is that you don't need to read in the whole file before you can start working with the data. This is great because it saves you memory (don't need to store the whole thing, your can store one line at a time depending on your specific issue), latency (don't need to wait for the whole file to be read and parsed, you start immediately after the first line), etc. Huge JSON files might be also too big to load into memory. You can read one line at a time, you can stream your lines, process your input across multiple computers etc. And, as it's just json lines, you also don't need to invent a new notation, specialized tools, etc.