The most common case is probably complex search queries. It's really nice not having to flatten your data just to get network level caching.

In my case, building an RPC library with REST semantics, it's important to me to not place any restrictions on how developers pass their data to the backend. So removing that arbitrary flattening requirement is a big win. The json-qs specification does it in a way that balances readability and compactness.

I just published it now: https://www.npmjs.com/package/@json-qs/json-qs