I've been out in the summer when it was just too hot to sleep on any type of mattress while the hammock was A-OK. In the winter they really need a pad as the circulation under can be too cool with just a sleeping bag. For wet conditions they keep you off the ground and dry (need a roof tarp) and especially if you're scared of snakes and spiders and scorpions. and DWA.
I have also tied them up between ball hitches on car bumpers (being close to the ground watch your axe), and have carried two six foot long poles to hang my hammock on when I knew I was going to have a hammer with me. When rock climbing, I've used climbing gear to secure it in rock, and I've even stretched my hammock between test stands out at FAR.
Do a search for free standing hammocks, for example
http://www.practicalsports.com/abo-gear.html
Rick