It depends.
According to a friend who is working in one of the Big 3 in Seoul, it will not affect most people.
The consultants at these Pre-MBA dinners/workshops tend to remember two people, a) the people who are really outstanding, or b) the people who really make an ass of themselves. The rest are usually forgotten until recruiting starts up again.
If you think you can really leave a good impression, then it helps. Otherwise, it's neutral or potentially harmful (unlikely, I hope.)
I went to all the events I could. At the very least, I got a nice dinner out of it, and I got to meet my fellow admits again as well.