Me I use it loud. But only when you start to see signs of the rut.
I use a True Talker Grunt starting around 7:00 am. I continue to
call with the grunt about every five or so minutes till I get an answer.
Then I reley on the can with off and on grunts about every ten minutes.
You have to watch the downwind side cafefully though because all this calling
will make them swing down wind. Try to leave yourself a good shooting lane
down wind just in case. It does help. Here are some sound files to help.
http://www.wideworldofhunting.com/soundsofwhitetail/WhitetailDeerSounds.htm
Good Luck,
Eric