What kind of animal is it, how to do it and when is it better to use this hint?
As I understand it is used to achieve resource savings?
Not really, if the conditions for this method are met, that is, the likelihood of less memory use.
If the assembly is loaded as domain neutral, then all application domains with the same security permission set can share JIT-compiled code, which reduces the amount of memory required for the application. However, the assembly cannot be unloaded from the process.
If an assembly is not loaded as domain neutral, it must be JIT compiled in every application domain it is loaded into. However, an assembly can be unloaded from a process by unloading all application domains to which it is loaded.