Dragon's teeth are one element of a defensive delay plan. It's never dragon's teeth alone, is dragon's teeth plus mines plus barbed wire etc.

The shape of the item itself is designed to get dragged under a tank, cut into the ground and then high point it. Which isn't a big deal by itself. But if there's observing fire, artillery, antitank weapons, infantry defending. Now it becomes a delaying item an extra obstacle that you have to deal with while assaulting a position.

A force multiplier

anti tank lines, not sure how usefull they are tho

I don't know the Russian military, but I think it's unlikely these were soldiers, contractors thinking they got a cushy gig away from the action.