Risks? Kids hate their parents because they are embarrassed in front of their peers. Their friends move on to the next grade, they stay behind. They are labelled as dumb by their friends. You also get another year to do their laundry, clean up behind them.
Advantages? Another year for you to save for college. Maybe you get your grass cut for another year. Maybe.
Strangely, it's the opposite. The kids that "redshirt" in 8th grade are known as athletes and carry a certain pride for redoing the year. Not everyone gets to do it, only the better athletes... go figure.