I've been working on some images for my next FAQ update, this will help explain the full floater axle a little better.
This is a standard semi floating axle shaft, which is what most axles are, the wheel bolts directly to the axle shaft itself:
This is a full floating axleshaft:
Back to the semi floating axle example. Here you can see the tire is bolted directly to the axle shaft, and the end of the shaft actually has to support the weight of the vehicle. The shaft is supported on the end by a bearing that is pressed into the axle housing.
Here is the full floating example again. A full floater axle can use a spindle with bearings like an old school front axle, or can use a unit hub bearing like newer front axles. Either way the bearing is bolted the axle housing itself, and the tire is bolted to the bearing. The axleshaft carriers no weight, and its only job is to transfer torque.
Pictures always help explain things better, IMO.
A full floater axle has some major advantages. Since a full floater axleshaft carries no weight, you can destory a shaft, and still drive on the axle. Changing a full floater axleshaft can be done in minutes without even jacking up the vehicle. Without the extra stress of the weight of the vehicle on the axleshaft a full floater shaft is also stronger. This is not to say that a semi-floating axle is a bad choice or is a weak axle, but a full floater axle does have some big advantages.