In the case of drivers, you always have to ask yourself why you want to update them and whether the rewards compensate the risks. In the case of the regular release drivers, it's advisable to update them unless you have reason to believe that it will break something you don't want broken. With beta drivers that's the opposite: you want to use them only if you have something not working and you have reason to believe that this beta version can solve it (and preferrably not break other software).
The key here is the concept of "beta" software. It's still not the final version. You can find more info on
http://en.wikipedia.org/wiki/Software_release_life_cycle (if you don't know already), but the general idea is that it is still subject to bugs and crashes and is not a finished product.
Hence, unless you have the need for it, it's generally not advisable to use the beta version.