This is a question we get asked quite a bit. The obvious answers, and the motivation for the questions, are most commonly related to things like "bugs" or "rain" or "snow" or "wind".
However, I have been wondering, and I'm wondering if others think about this as well, whether the weather protection (e.g., from rain, wind, snow, etc.) that is purchased by the additional weight of a single wall tent over, say, a tarp+bivy combo, is worth it?
I find myself tarp camping primarily in the summer, where even in the mountains, the weather is not a big issue and I simply can't define a lighter sleep system than a poncho tarp, a Vapr Bivy, and an Arc X.
In April and October, however, I begin to think a little harder about these questions.