From the manual:
auto_globals_jit
Default: "1"
Changeable: PHP_INI_PERDIR
Changelog: Available since PHP 5.0.0.
auto_globals_jit boolean
When enabled, the SERVER and ENV variables are created when they're first used (Just In Time) instead of when the script starts. If these variables are not used within a script, having this directive on will result in a performance gain.
The PHP directives register_globals, register_long_arrays, and register_argc_argv must be disabled for this directive to have any affect.
It's effects aren't like the effects of register globals, so it should be fine if on... So, take what you will out of it...