Most outdoor enthusiasts that use bivy bags instead of tents because they prefer the lightweight and compressibility of bivy bags since they give you far less to carry and don’t take up as much room in your pack. Bivy bags are made to be smaller, easy-to-use and easy-to-carry sleeping shelters that are made to keep you warm and protected from the weather.
Although bivy bags are very popular among outdoor enthusiasts, some backpackers do prefer lightweight tents to bivy bags. However, when comparing bivy bags to tents, you’ll find that they are much easier to set-up and far more compressible and lightweight than a standard tent. So, if you’re simply looking for a one-person shelter to protect you from the outdoor elements, then there is a good chance you’ll prefer a bivy bag over a backpacking tent.