Nothing.
It's sort of a long story, but GlassFish was once intended to be
integrated into a suite. So the top level that has the "glassfish"
directory also has "javadb" and "mq". The "bin" at that level is
intended to be for the more significant CLIs. The glassfish/bin
directory has all of the CLIs that are provided with glassfish. asadmin
is in both places.
Tom