Features of Hermes
Ahead of time compilation. Hermes is developed for fast startup.
Hermes helps the React Native apps to decrease the memory usage of the device and thus resulting a smaller app size.
As per the need bytecode can be mapped and loaded from the flash memory gradually.
In chunks an on-demand virtual address space is located to avoid the need of estimating the heap size and overhead minimizing. And the free memory can easily be returned to OS.
Hermes targets ES6, which is now not being used in the React Native applications.