I've actually watched a few of those. They're not quite so bad (yes they are bad, but bear with me) when they're done by music professionals as at least you get something resembling an informed opinion, but I drew the line when I saw one in my recommendation list in which a beauty therapist or some such was supposed to be reacting to an acappella song (which, let's be fair, is a bit off the beaten track to start with)...