There are a lot of areas in caves and in buildings which are extremely dark and easy to get lost in. Seeing in these dark areas can sometimes be solved by turning up the in-game brightness beyond the recommended setting, however when you take into account glare on the television screen it can still be very difficult to see what you're doing. On more than one occasion I've gotten lost or stuck in a cave or building because of how dark it is and had to have a friend come and find me and lead me out, or fumble around on my own for five minutes or so. Seeing as a flashlight automatically enables during pitch black areas (like the Hive breeding grounds just before your first encounter with a Hive Wizard) I don't imagine it would be too difficult for Bungie to add a manual setting for turning on the flashlight. Perhaps by pressing the touchpad in to bring up the Ghost and then tapping/holding the circle button. If there is a reason why the devs can't or don't want to add a manual flashlight then I'd be very interested to know why.