I've never done it but if I had the money or opportunity I would. Honestly I don't think there's much benefit other than satisfying curiosity. Theoretically you can learn more about your dog's genetic medical history or temperament but unless your dog is a little puppy you probably know some of that already.
I did this recently with a dog I adopted. I had so many ideas of what she could be, but knowing for sure has helped me in knowing what personality traits to accept as normal and how high of a stand to hold with obedience, learning capabilities, etc. Also possible heath conditions. I love my pure breed German Shepherd so I was really happy to find out that my dog was 50% GSD 25% min pin 25% chihuahua... at 25 lbs shes literally a mini German Shepherd
It's fun. And funny. I did this once a long time ago just for the fun of it, plus I had gotten a great deal on the Wisdom Panel test, got it really cheap! I had guessed my dog was a Chihuahua/Pug/something or other mix, and got back: Cocker Spaniel, German Shepherd, Pekingese, and Italian Greyhound.
....for this dog:
For the area I lived in at the time, I kinda don't believe it! haha! (Italian Greyhound is believable though, but I've never seen one in that town.)However, it was amusing when someone asked her breed to say "Oh, she's a German Shepherd/Pekingese mix! or some other variation of the four breeds Wisdom Panel assigned to her.
I have heard that if you are given an unbelievable result that they will run the test again, but I never had it rerun. Too bad they're so expensive, otherwise I'd have my Collie tested to see what they called her! onder:
There's a member on this forum who has a blog I follow. He just posted about a newer DNA test that tests for a few different things:
150+ Dog breeds
160+ Genetic diseases and disorders
Wolf, Coyote, and "Village Dog" ancestry
According to reviews it's the most accurate and extensive test out there
It sounds super cool but it's also a lot more expensive than Wisdom Panel! If I had the money I'd be interested in trying both and then comparing the results.