[Solved] Question about RegWrite()

The function documentation states "When running on 64-bit Windows if you want to write a key or value specific to the 64-bit environment you have to suffix the HK... with 64 i.e. HKLM64"

   I am a little confused about "a key or value specfic to the 64-bit environment". What does that mean? Is it saying use HKLM64 on 64-bit Windows or just on certain keys and values?