Putting the tractor FEL in "float" takes all hydraulic pressure off the FEL as Kennyd states. The arms (frame) will essentially become limp.
However, the bucket will hold its tilted position and, on most FELs, will still curl and dump.
So for backdragging and spreading gravel, dirt, manure, etc. just set the bucket at about 45° to begin with, put the FEL in float and spread the whatever by hooking it on the bucket's lip and dragging backwards. The angle can be adjusted for more, or less, aggressive spreading. It might have to be done several times for large piles.
Then, at the end of the drag pull back and out of float while raising the arms. With practice, you can curl the bucket at the same time and leave a nice finish at the end of the spreading.
Some folks use float for snow removal but I'm not familiar with the technique. No snow here. (Sorry, Easterners.)
Also, when parking the tractor, putting the FEL in float will take off all pressure and it seems to be better on the hydraulic seals. The bucket will sit on the ground so, if you are worried about that, you can put down a brick or block for it to rest on.