About not using a tent, mainly I'm lazy. I don't like the weight of tents (well, any I can afford). I don't like the time and trouble of setting up a tent. I don't like trying to find a spot big and flat enough for a tent.
Personally I like the versatility of an Army poncho. It's good wearable raincover, it can snap into a sleeping bag shape, works as good groundcloth or lean-to cover, and if a companion has one too, they can be snapped together to form a larger shelter. They are fairly compact and lightweight. The addition of the poncho liner makes it even better for sleeping.
Regards,
Tom A.