Jnana wrote:Vipaśyanā generally requires some degree of śamatha. The latter is most effectively developed through sitting with the back properly aligned. Thus, sitting meditation is conducive for the arising of vipaśyanā, but it isn't essential. Vipaśyanā can arise while engaging in any of the four postures.
Regarding samatha, it depends on the specific method. In relation to mindfulness of breathing, the Buddha explicitly recommends sitting -- in the Satipatthana Sutta (MN 10), for example, the meditator is described as sitting down, legs crossed, keeping the body erect. It can be practised without an erect back -- even lying down -- if circumstances are such that the meditator cannot sit, or cannot sit with an erect back, though it is more difficult in the beginning, requiring more intense initial concentration. There are many samatha practices which are not dependent on posture and which can be taken through to jhaana in postures other than sitting, though it is presumably difficult, dangerous and therefore totally impracticable to achieve jhaana while walking. A posture in which one can be still is therefore probably a prerequisite for samatha, taken through the jhaana. When not taken through to jhaana, it is a different story. Vipassana, as distinct from the jhaanic content of samatha, will not be hindered by movement; but it will be helped greatly by the focus which immediately prior practice of the jhaanas brings.
There is one statement in this discussion in relation to which I agree with deepbluehum, but suspect that you will also agree with it. Samatha and vipassana should not be viewed in isolation from one another, at least from the perspective of the Buddha's teaching in the Suttas, but instead should be seen as two aspects of a unified system of practice, samatha-vipassana, in that they go hand-in-hand and cannot be divorced completely from one another in the path taught in the Suttas. The Buddha's description of mindfulness of breathing in the Anapanasati Sutta, for example, sketches out an integrated development of the practice which runs through jhaana, into insight and through to the ending of the fetters.
All of this is invaluable for people seeking to practice Dzogchen. Something which my teacher, ChNNR, has been recommending lately is that people dedicate time to what Theravadins would call the practice of sati, simple straight-forward mindfulness in daily life -- being in the present and going about one's everyday activities with mindfulness -- integrating this into Dzogchen practice.