Not sure about working for long uninterrupted sessions(I tend to believe that short, self-scheduled breaks increase my productivity, as per the pomodoro technique), but I think the notion of loading a 'context' into your memory is spot-on. I know that, at least for me, it is difficult to even begin working on a problem unless I have that initial context in my head; without a full understanding of the problem at hand, I feel like I can't do anything well.