WHDLoad basically circumvents the operating system in the Amiga for greater compatibility and preserves the original program environment.
The primary reason for this loader is that a large number of computer games for the Amiga don't properly interact with the AmigaOS operating system, but instead run directly on the Amiga hardware, making assumptions about specific control registers, memory locations, etc.
An added benefit is the avoidance of loading times and disk swaps, because everything the game needs is stored on the hard drive.
These slave files are freely available from the Internet (as Freeware), but the games themselves have to be acquired separately, to prevent software piracy.
If the Preload feature is enabled into the requester page of WHDLoad, then the program attempts to load disk images and files into RAM (insofar as free memory is available).
At this point, the program that has been installed can perform the task for which it has been written, loading its data as it would from a real floppy disk.