IronSpike
Deviant Art is a convenient, low-hassle platform for creating a portfolio when you can't be bothered to buy your own space and learn basic HTML. That is its only good quality.
Beyond that, it's a paradise of asspats, meaningless teenybopper drama, artistic stagnation and endless fan and fetish art.
While I agree 90%, I don't believe that is the only reason for using deviantArt.
While the quality of criticism is not the best, it can be used as an additional resource for receiving a critique on your works to improve--also, if used properly, you can help refine your abilities by finding other successful artists doing what you're trying to do.
I've swapped ideas with people on there about the best way to make armatures, paint clay, baking it, etc. And I would not have been able to get any of that insight on a self-made hosted website.
And if anyone seriously uses dA as an outlet for portfolio making needs to be shot. That is not a place for a professional, or someone wanting others to see them that way.