While groundsheet protectors for inner tents are not strictly necessary, they do provide some advantages. Obviously they provide a layer of protection for the groundsheet and keep it clean. They also provide a layer of insulation.
This is useful with thin groundsheet material like Chikara. In conditions of heavy dew, moisture can form on the inside of the groundsheet especially under mats and stuff sacks. One way of avoiding this is to use a groundsheet protector.
I’ve found using an Adventure Medical Kits Emergency Blanket particularly effective. Unlike old style emergency blankets, it’s silent and quite tough, like strong polythene. The silver reflective side helps insulation and, in most cases, eliminates dew.
Yesterday I cut a survival blanket to make a groundsheet protector for my OookStar. It’s very easy to cut neatly with sharp scissors. I put some small strips of duct tape at the front to aid alignment. The protector weighs 55g in all, which is a small penalty for extra protection and comfort.