Its true that your eye adapts with the lights and the more you are used to using the flashlight it'll get blind dark once its out, so the premise is that if you adapt to the darkness you'll have better time with surroundings.
But a human eye can only use so much light thats available to help them see. Even in a full moon light, when its in a closed building relying on your eye alone is not gonna be a good thing its just better to use flash light and see detail's you need to know instead of getting superstitious in what you see and mistaking a lot of things.