Restores common sense and trust
My children are at primary school and we are forever having to sign pieces of paper to give permission for lots of things. E.G Going to local swimming pool for lessions in school time
I totally trust the school to do whatever is required and feel I do not need to give permission all the time.
A similar thing happens at Brownies. If for example the kids are going out to play in the park instead of all meeting at the church hall, a permission form needs to be signed.