According to the guidelines registering long arrays does not need to be turned on for Moodle 1.9.x.
The questionnaire modules instructions says you do need to turn it on.
The php.ini files suggest this might impact on speed and is not recommended for a production server.
Thoughts please. Does it impact the speed of the server significantly? Does the questionnaire module still need it or is it an old instruction that can be safely discarded?