No real benefit, other than I got to meet and hang out with people outside of my usual social circle, but it depends on the school and how the fraternity is organized. The dental frat 'scene' at UOP is generally a ski trip or two, a bunch of sponsored lunch and learns, dinner lectures, and the occasional party. We just don't have enough time for shenanigans. The one tangible benefit I can see from my experience is that I was able to network with dentists outside of the UOP bubble.
I think that the social, professional, and academic/continuing education roles that dental frats aspire to fill will be filled anyway by the people you meet when you're a practicing dentist. They can give you a starting point for networking etc, but you're going to naturally gravitate towards the people you trust and like.