The only advantage you would get is speed. However, you are now working with two HDD (asuming you want to go RAID 0). The information you will read/write will be spread over these two HDDs. This being done, you need to take into account the failure rate of BOTH HDDs, not just the one that you have now. Hence, there is an increased percentage in the likelyhood that you will experience a HDD problem (because we're dealing with two HDDs not one). Because the information is shared between the two HDDs it would take a fix to BOTH HDDs to resolve some of the more serious issues that could come up. This is why your data is at a greater risk when you do this. RAID was originally developed for a networking environment where the speed of your HDD read/writes is crucial to the performance of your overall network.
256 chickens that can say "bok" simultaneously while laying eggs asynchronously in 64-bit glory.