The point is to add complexity to low levels, which are typically devoid of complexity and boring while also encouraging more group play. At low levels, the amount of complexity you can add to the game is limited because players lack the tools to combat complexity. You can't have meaningfully powerful enemies because the only solution players have access to at low levels is "smack it with more people." For the question of "how do we increase low-level interaction with the world without increasing their access to tools," the answers are "don't handhold navigation" (which I won't get into in this post) and "darkness." Darkness specifically creates a resource management consideration (torches) and also encourages group play; if you can't carry a torch because you use a shield or two-hander, group up with someone who can hold a torch or has infravision (dual-wielding classes don't get access to dual-wielding until level 10, by which point there are more solutions for the darkness). This is a meaningful way for low level players to interact with additional complexity while also helping to create a torch-bearing niche for classes that typically can't carry torches.
If you're using torches and you still feel like you're blind, then that's probably a graphics issue that the gamma slider will be able to help. While I was using torches, I never felt blind.