Rapid mode is a feature of samsung ssd's that you can turn on in samsung magician. It uses 1gb of system memory for faster caching of data before dumping it to the ssd itself. It increases read and write speeds by quite a bit, though most of it is artificial (i.e. it has most of its effects in synthetic benches). It doesn't really seem to do much. I don't notice a difference. If you are video rendering, apparently it really helps, but I'm not doing any of that. I guess I'll just leave it disabled. I just wanted to post on here in case anyone had any experience with it one way or the other.
if you have a fast enough disk, then RAM cache (aka rapid) makes no sense, it used to make sense in the old days of spinning rust disks, where seek time was limited but SSDs were insanely expensive - any that's why hybrid disks were invented, (and why disks like hyper OS hyper disk were invented)...
now... with Sata 3 speeds on solid state disks, unless you're doing something insanely intensive on the disk, you just won't notice...
on the other hand, unless your system is packed with RAM you probably will notice the resources reserved for that being missing.
Long story short, I can't see a great need for it today, most people want their ram to handle volatile data, (and want as much ram as possible so they don't end up caching volatile data to disk, and their disk to store, - and they don't want stuff that they definitely want saving stored on volatile memory.
it's one of those, sure try it if you want things, but I could genuinely see it going wrong for people in the case of power failures etc.