WITH_LLD_IS_LD vs default WITHOUT_SYSTEM_COMPILER: What are the reasons?

[Mark Millard]

man src.conf (from -r315914 ) reports:

     WITH_LLD_IS_LD
             Set to use LLVM's LLD as the system linker, instead of GNU
             binutils ld.

             This is a default setting on arm64/aarch64.  When set, these
             options are also in effect:

             WITHOUT_SYSTEM_COMPILER (unless WITH_SYSTEM_COMPILER is set
             explicitly)

I'm curious about:

A) Why there is a bias to avoid the system compiler?

and by contrast:

B) What sort of context justifies explicitly setting
   WITH_SYSTEM_COMPILER when WITH_LLD_IS_LD is in use?

===
Mark Millard
markmi at dsl-only.net