Think of it as a runtime + scheduler that you deploy programs to ESP32 devices. It gives you the ability to run multiple programs simultaneously (with isolation) and remote updates. The language compiles to bytecode; the developers have lots of experience writing VMs for constrained devices; see https://www.theregister.com/software/2004/07/27/forgotten-la... for something that predates V8 and Dart.
Tangent: what an appropriate username :)
You get almost all of that with the more common language options too (MicroPython, NodeMCU/Lua, Espruino/JS). What makes this custom language better?