I usually ask a commission to help out an artist. Though it depends on the need. Best example: I've found artists who want to attend a convention, they need money so they take commissions...I don't really support that.
But when I find an artist, whom I know I can trust, tell me they are trying to raise money for their wedding and/or honeymoon trip. I will gladly chip in.
I feel there are some things, to important to miss out on. Such as a wedding, a honeymoon, charity for helping out another artist in need. Those type of events are a once in a life time rarity. Events such as conventions are once in a year, nothing as extravagant or important in life.
the number one thing I find is DA is no good for commissions. DA is a popularity contest, plain and simple, and unless you're one of the chosen few, you're not going to get them.
Arguably, when I had a job, I commissioned several people who needed the money, and even donated to another, but I'm once again on financial aid and back at school, so I'm back in the same boat.
My roommate says she has gotten commissions from reddit and sold prints at redbubble, two sites which I'm thinking about trying. But DA is really not the place to pimp yourself. There are a number of people on DA who are jerks (heck, there are a number of people on the INTERNET who are jerks).