It's also quite dangerous if you haven't taken physical preparations beforehand. To sit on the floor 6-8 hours a day with a weak westernised body, used to sitting in a chair, is dangerous. If your not super fit and have great core strength, the muscles around your spine simply can't hold you for that long and you collapse into the skeleton, which can lead to injury. Traditionally, Vipassana would have rigorous physical training before the meditation, now in the westernised setting, we just go from sitting at desk 8 hrs a day for decades, to sitting on the cushion.

Furthermore, the endocrine system can get really messed up when you sit for that long over a number of period of days. When the body doesn't move, things stagnate and cause problems (just look at all the research coming out about the dangers of prolonged sitting)

However if one is physically fit & ready to begin, then great things can happen!