Personally, from what I experienced and witnessed, I do not think that there is much benefit of practicing dzogchen as a complete beginner (unless you are that extremely rare prodigy, as someone else mentioned). The first time I practiced with a group, that is, doing anything but reading and talking conceptually with others on my own, was with a Dzogchen group. The first day in the door, without any explanation, I was doing a Vajrasattva sadhana. Up to this point, my reading had mostly been about Zen & Taoism, so I was pretty much totally unfamiliar with Tibetan Buddhism. I didn't know if Vajrasattva was a god that these people worshipped or what the hell was going on.
I can't remember the sources right off hand where I've read about this, at the moment, but I believe traditionally that no one ever started practicing Dzogchen right off the bat. People came to it only after much study & practice within hinayana and mahayana- even if these were presented from a vajrayana perspective. Even besides the understanding of the view, I don't think my mind was properly settled to even attempt sadhana practice, or resting in ripga, without many hundreds of hours of shamatha practice.
This is just my two cents, and perhaps some people are better off just starting with Dzogchen, but I would recommend being grounded in sitting practice, and the study & contemplation of hinayana & mahayana topics before moving to vajrayana.
Also, and unfortunately I don't remember the source for this either, but I heard a teaching from someone saying that when Tibetan teachers came to the West they were in awe of Westerners because of our highly advanced technology and complex society. So, they assumed that we were highly evolved and that we could be taught the highest vajrayana teachings. They didn't want to insult us with the basics. So, when Trungpa Rinpoche came here in 1970 he was teaching vajrayana- mahamudra & dzogchen. But, then he realized that nothing was happening. It was because no one was grounded, people's minds were wild & grapsing (spiritual materialism) and he realized he had to start from the beginning, make people sit, study the abhidharma, and essentially learn how to be decent sane human beings first.
But, of course, it's not like we master or complete the hinayana or the mahayana before moving on, when we're practicing vajrayana (in Trungpa Rinpoche's lineage at least) we're practicing all three yanas together. But, there is a lot of preparation done, a lot of taming & training of the mind before one goes on to the higher teachings.