On an individual level, it usually isn't wise to hold too many stocks or bonds in ones portfolio. While it's good to have some stock holdings (and potentially even more bond holdings) it can be very dangerous if one has too much invested in either. However, balanced funds can fall somewhere between these two other types and thus make a good choice for most.
For individuals, stocks and bonds can both be very risky investments since stock values can fluctuate wildly while bond values tend to stay steady or even decrease in some cases. On the other hand, some balanced funds seek to use their assets more effectively by investing in both stocks and bonds. This helps to mitigate the risk of one or both by diversifying their investments.
With the stock market being so volatile, this is seen as a positive thing since many investors are often unsure about how well or poorly it will perform in the future. Balanced funds use their assets more efficiently than if someone had just invested all of their money in either a single stock or a single bond. With balanced funds, one should expect to receive higher returns that what they might have gotten from just stocks or bonds alone.