We hate them too. If you put them in when the lambs are very young, they can make the ear flop, and/or pinch as they grow. If they are in during the fly/midge season and there's any discharge - they don't have to be newly applied for this, either - then that attracts the flying / biting / egg-laying insects... If you get ones that don't come out then you get ripped ears, and the damaged ear becomes a fly / midge magnet...

Far better for animal welfare to put them in only when the animals are being sold on. I suppose if they are younger animals being sold on for breeding, this isn't much consolation anyway, they can still have all the same problems, just in a new home.

Pic is of a ripped ear that had been mangled further by the attentions of flies.