I don't usually do this. I can't remember the last time I did, though I'm sure I've done it at least once and didn't like it. It goes against my nature. I am very organized and I plan out my stories as best I can before I write them. The very essence of this exercise is chaotic, and naturally a polar opposite to what I'm used to.
Although some say it can be good to get content out of your subconscious, I believe it will more often just be a literary vomit of whatever is within your short-term memory, aided by a train of thought to whatever is relevant to the previous word. It can be a fun exercise, but I wouldn't put too much weight behind it, personally.
If you're looking to try it out, you should do so and post what you write here. People may join you.