When did they introduce that? That doesn't sounds like a good idea.
I don't really know. However it might be regional(my impression is that CMAS isn't a homogenous agency), up here in sweden/scandinavia. I do know that it was one reason a friend of mine's mom picked CMAS over PADI. The reasoning I'm hearing is that it prevents buddy separation, and that many/most accidents have buddy separation as a factor. Then again I'm also hearing a lot of agency bashing from her... directed at the agency I teach for; as well as some things she's said that don't seem so good to me(she's been surface cover, and has no training, for example).