I've been into off-roading for a long time and lowering the air pressure is common practice for better traction. Seen several people make setups for either 2 or 4 tires (as mentioned above many people run different pressures front and rear).......most of them stop using those contraptions after awhile because it usually easier and about as fast to just do each tire separately. Seems like it takes forever to drag that type of contraption out, untangle all of the hose and get them hooked up. When inflating the tires they don't air up any faster as the compressor only puts out so much air....inflating 4 tires at a time takes 4 times as long as inflating a single tire. Might deflate the tires a little faster, but only after you get it all hooked up and then get everything unhooked and put away.
For an above comment about it getting a leak and waking up to four flat tires.......you don't leave it hooked up to the truck overnight. You only have it hooked up when actually using it and the truck obviously has to be stopped at the time. You can't drive around with it hooked up!