This is all about when the cache gets flushed. It can be a performance item, but there is a RISK of not flushing it fast enough, data could be lost. On a busy system if it is OFF you could get into a situation that you'd power down before the cache gets flushed. Rare, but it can happen. Of course a loss of power would be the more likely case to cause this.
I'm on W8 now and I can't even find that stuff to check? I know it is somewhere?
Check these links though...
It is all about data integrity vs. a small performance boost.