I always prefer sleeping under the stars if it's not raining - I find the view before falling asleep somewhat better than in a tent.
As has been mentioned dew can make the outside of a bag very wet. For this reason I always use synthetic bags.
An inner liner is useful not only for extra warmth and keeping the bag cleaner, but on hot nights lets you open the bag and still keep them mozzies off... I use repellant on my face and neck if the enemy are out in force! I actually use double liners, one cotton, one thin nylon to get the balance just right... It seems like mosquitoes have evolved since I started travelling in the '70s to have longer hyperdermics, and that they are thirstier now than ever before. Any scientific backing to this? Cyccocomute??
For me, weight is a non-issue. I love sleeping well.