Sounds like someones's sensei was tired of them dodging gradings & fixed it... ;-)
ha ha ...yes - I've seen that approach deployed ;-)
As others have posted, both approaches have their merits.
Personally I'm in favour of using announced gradings to encourage the extra focus among those in the frame but at the same time we are not all the same ...If you leave some people to grade when they think they are ready they will never be ready.
So helping them help themselves is called for.