I read the guy sent a letter to a magazine (to explain the use of this tool) saying that for him, waking up in the middle of a cold night to light a candle and write some ideas or parts of his creations was not suitable because too many facts like, for example, texts written in plain English in mid dark were not legible the upcoming morning for him (ink based devices to write and the guy was sleepy) + sometimes the ideas were so brief that waking up to go to a desk got him to forget the idea completely so this device was used right from his bed without the need to wake up. Apparently he slept with this tool behind his own pillow. It was easy for him to use it i guess.