There were a few things going on in my daughter's situation, which sort of goes back to the point of Leslie's article. Trying to piece out a "practical" answer vs. one of a "paranormal" nature.
For one, she seemed to be freaked out by a shadow on her wall. Can't blame her, I'm 30 and not really a fan of shadows, especially when I can make shapes out of them. In this case, her nightlight was behind her end table, which has a table cloth on it and a white noise machine on top, and the combination sort of looked like a cloaked figure. Move the nightlight, turn on one of her room lights, and voila, no more shadow.
The "spot monsters" were a little more tricky, especially with her claims that they were moving her toys. That's were the smudging and cleansing rituals came into play.
As far as the light being on goes, if it makes her feel safer and more secure in her space, then yes I think it helps.