I carry a Sea-to-Summit sil/nylon poncho in my EDC bag for the size and weight. In my hiking or camping backpack I will add a military poncho or 2 just because they are more durable and a LOT cheaper.

I have some tarps as well, but generally carry the ponchos as they are more versatile. It depends on where I am going, who is going with me, and what I am doing.

Sometimes you need a vapor barrier between you and the ground, sometimes you need overhead shelter, and sometimes you need both.

But for camping in swamps, nothing beats a hammock with a poncho hooch overhead.