My basic conviction is that the more deeply personal and honest the work is, the more it will have resonance for other people. And so in any form, if the writer can sublimate herself completely within the object of observation, it is probably a good idea. It always has been. It's where prose shines. Perhaps the most important discovery for me through writing creative nonfiction has been finding ways to combine scenes and images and different elements of writing without explicitly connecting them.
Every writer has different means of getting there and staying there.
For myself, I rely mostly on books. It was pure sound, unencumbered by sense. Some days I read part of any poetry anthology's index of first lines. The parallels sounded strong and suggestive. They could set me off, perhaps.