IMHO it is only to show, that there is "BAAAAAAAAAD" over (under?) there. It was, and apparently is, used to help people build a vision of hell, by using things that people are afraid of. Fire will make you suffer, it is going to burn you... slowly. Because of heat you will not be able to breath, it will burn from the inside - YOU WILL SUFFER. Darkness will make you scared.
And, of course, there has to be someone that is opposite to God, someone bad, "supervisor" of your suffering. And there comes the devil(s).
I think of Heaven and Hell as a state of mind - how you will feel, what is going to bother you, it will not let you forget about the bad thing you have done to others, you will feel bad, really, really bad - that kind of suffer.
life is beautiful...