When you go to high school you go to learn your subjects. Not get pulled out of classes to man desks. Why? Is there not enough staff, or something? I suppose it would be easier to get the kids on there manning the phones. You don't have to pay them
when my children go to high school they'll be going to learn their subjects & also preparing for adult life.
It's two hours, twice a year, in which I think they'll learn rather a lot, with an expectation that they catch up with class & homework missed.
There's no question of it reducing the office staff's workload - they like having the kids in, but it's definitely an extra call on their time & patience.
As a teacher & year 7 tutor, I think it's a great learning opportunity (& believe me, it makes extra work for me, too, to organise the rota!). As a parent, I'd absolutely support my own dc having this experience.
But if you disagree, I'm sure you could decline the opportunity for your own child to be involved. As I previously said, this very occasionally happens where I teach, & is in no way a problem.