I think mainly as a C replacement, for added productivity. Compared to Node.JS QuickJS seems to interoperate with C. Node.JS standard library is fully async, while QuickJS use C standard lib. There's also GnomeJS which can be used to build apps that looks and feels like native apps, maybe you can also do that with QuickJS!? Being able to obfuscate the code by compiling is also considered a feature, useful when you want to distribute an application without giving away the source code.

A very small and fast javascript interpreter. It will create a small library file for the programs who depends on this and according to the benchmarks it runs faster than the other javascript interpreters.

If you want a very fast javascript engine and dont have problems with binary size, memory constraints and executable memory pages, you can pick a JIT like V8, Chakra or Spidermonkey. As those JITs are pretty advanced optimizing JIT compilers and will run javascript code very fast, much faster than the fastest interpreted VM implementation can.

People who tend to choose this instead of V8 for instance need to run this in a microcontroler for instance, or a OS without executable memory pages (and therefore where JIT´s are forbidden).

also can be embedded in a microcontroller