F-bob makes a good point.... many ppl who have enough "real estate" on a touring bike's steer tube will mount 2 stems, and use a narrow flat bar on the second stem to mount various accessories (eg, headlight, computer, various other electronics, bells, horns, a compass, a bag, etc. ) Basically, it gives you some room for your stuff, leaving your handlebar free to fit your hands and the bike's controls.

http://mgagnon.net/velo/potence-double.en.php

http://api.ning.com/files/GxNVrf8kg9...t_lights_3.jpg