My experience has been its a short term somewhat euphoric high that makes everything feel a bit tingly. Similar to the gas a dentist gives you. Not everyone's cup of tea, but it can be interesting.
To answer the question - I guess its the same reason a lot of people drink alcohol, or take other substances - they like the effect.
Also it would seem like a relatively low risk drug, particularly when compared to some of the pharmaceuticals which seem to be far more accepted on these boards.