As stated above it's adding/removing an HDD (or SSD) while your PC is powered on. It very usesful for data back-up and disk mirroring. Just pop in an HDD whenever you want to back up something. Because it's a direct SATA connection (vs. E-Sata or USB with external drives), there's no potential issues with OS drive cloning or firmware updates.
Whether you can hotswap reliably depends upon your OS. Win 7 was built with hotswapping in mind. Not sure about Vista, but I think it's okay. Some people can hotswap running XP, but I never got it to work.
If you want to enable hotswapping, you need to set the SATA Configuration in your bios to AHCI from IDE, however
I've read that at least for Win 7, it's best to set to AHCI in the bios prior to installing the OS. It might be perfectly fine to change it afterwards, but I suggest doing some research on this first and back up your data as well.
I have an FT02 case which is almost identical internally to your case. The hotswap backplane can be removed if you want. The problem with the Raven2/FT02 is that you have to remove the side panel to get to the HDD cage and use the cases HDD bracket for every drive you want to swap which makes hotswapping a lot
less convenient than cases which have front panel access (800D) or an HDD port at the top of the case (various CoolerMasters).
That's why I never installed the backplane in my case. Instead, I installed a 5.25" front bay single HDD rack
. Takes me less than a minute to swap out a drive. Finally, get HotSwap!
. It's makes swapping very fast & easy. Between it and my front bay rack, I can hotswap drives in/out in less than a minute.