yeah, a lot of people like it, but personally I don't. I will go with a single layer hammock next time.
the double layer can be used for mats or other insulation (dry leaves if nothing else is available), but I find that I can adjust and feel my mat more easily when it is in the hammock instead of between the layers.
on the other hand, the double layer really got me out of a sticky situation when I was in Sweden.
I was hanging over some sharp rocks, but just a little too low. A littlebit of stretch in the webbing made me hang a couple of inches lower than intended over the night and the rocks scratched through the fabric of my hammock, which totally ripped. luckily, it was the bottom layer and my sleeping mat was in between the layers, so the top layer and my sleeping mat were intact.
Had I been in a single layer hammock... well, it would have been a nasty wakeup for me