If you leave it anywhere in a bag not plugged in, then you have to be constantly thinking 'I only have 30 hours left till the battery dies and I lose everything I had open'.
I'm not 30 hours away from electricity very often, to the point where it wouldn't be a big deal to just save and shutdown, since it is a rare occasion. But I live a very predictable lifestyle, I guess if you are exploring London you probably end up in unexpected situations often.
Not a great feeling.