Cults have rules like that to cut you out of your old life, but in this case I think it's a legitimate desire to eliminate ALL distraction. I did one of their retreats many years ago and concluded that the changes in my internal life that could only happen in such an environment.

For example, after a few days my internal monologue petered out and for the first time I realized that a good portion of my mental activity was normally devoted to thinking about things I was going to say later on. Once I was out of the habit of talking all the time, I stopped cooking up little quips and observations about everything and really felt an expansion of non-verbal thinking.

So, although I had my doubts about the place going in, I left feeling that 10 days of intense internal focus was the only possible way to reach the insights I'd had, and that I was glad I'd done it. The months afterwards (while I kept up the practice, before I got "too busy"), were the most contented of my life.