Update - November 2018 -
While I used and appreciated Rapid Mode in the past, I personally no longer use it because a very affordable upgrade to a current generation SSD makes it irrelevant. New SSDs, especially on faster interfaces that support NVME are more than 10x as fast natively than the older drives that support Rapid mode.
Windows continues to get updates every few months, but there is minimal incentive for Samsung to continue to patch and evolve the Rapid Mode driver. At this point in time, if your budget precludes an SSD upgrade to one that is natively 10x faster, you have already decided that performance isn't that important to you, thus for the sake of reliability, I would now recommend not using Rapid Mode if you still have a drive that supports it.
I still believe it made sense and benefited some workloads at the time it was introduced, but the market has moved on, and it should now be considered obsolete. If you still run one of these older drives you can no longer claim to need the best performance possible, and should instead just maximize reliability for the remainder of its useful life.
__ end update __ - original historical reasoning follows:
I've found Rapid Mode to be noticeably beneficial.
How many of the other answers have actually tried it?
Working with large projects in Visual Studio all day, I have seen a noticeable improvement in build times and application launch times. Every second saved here contributes to my bottom line output and ability to remain focused between transitions. When build and run times increase even by a few seconds, it increases my odds of getting derailed with some distraction and loosing my flow. RAPID mode has made a noticeable difference and keeps Visual studio much more responsive.
Outlook is also noticeably faster - especially when handling my "error" inbox with 100,000+ items in it representing the last 7 days of my application errors. (yes, I know this is a logging anti-pattern - but it's what I've got and enabling RAPID mode has made it better.)
My Dell laptop has 32GB of RAM so I don't miss "losing" up-to 1 GB of RAM that this caching driver might use.
Having a name brand PC with wide market share means my system drivers are very stable. I've not had any driver conflicts or issues with rapid mode drivers whatsoever. Homebrew PCs may tell a different story.
I'm using windows 10 and the latest firmware and rapid mode drivers - things may have improved with any of these variables in the three years since this question was asked and the completion of the TechReport analysis referenced above.
My workload (code compilation, execution and debugging) involves reading and re-reading lots of small files, which is an almost perfect use-case for this type of smarter-cache technology. Gaming and media uses may not benefit nearly as much.
To clarify some points made in other answers:
Risk of data loss?? - Overblown - On a laptop with a built-in battery (UPS) this is a non-issue to me, and even on a PC this issue is overblown. Windows caches writes to internal drives in a similar generic way. So you have the same risk - but the windows implementation is not able to take advantage of the specific characteristics of a certain line of SSD, like the RAPID Mode driver can. No added risk here only added benefit.
It's true in the event of a flush command from the application that just having another filter driver in the pipeline is going to take possibly a few more nanoseconds longer to pass through, so this extends your opportunity window for data loss given a system failure by an almost immeasurable amount on top of a very small risk - but I'd wager that most anti-malware products with similar filter drivers are going to do their thing and take much longer to get out of the way of a flush.
That said, If you are running a database server or FreeNAS node, or any high-availability or unattended service, don't risk using Rapid Mode, but in a single user scenario this is simply a scare-mongering non-issue.
Doesn't windows already do this?? - Not as well, and not with regard for SSD characteristics.
Windows will use some extra RAM you may have to cache recent I/O, but in a very generic way. For example, reading large media files will blindly push other more useful things out of the cache. The "Rapid Mode" driver is smarter and looks at file types and historical read frequencies to potentially be much better than the windows cache under many common scenarios.
Of course the 10x+ difference in I/O benchmarks aren't going to translate into a 10x real-world difference in how fast your PC feels.
I have experienced a noticeable improvement in responsive "feel", and I appreciate this option on my Samsung SSD. I've had noticeable benefits and no drawbacks to using this option, and will be leaving it enabled.
No, I'm not a Samsung shill and it looks like Samsung has moved on from bundling this type of software anymore as the new drives don't support it and are fast enough to not need this kind of caching.
If you do ever have a BSOD that mentions
SamsungRapidDiskFltr.sys then of course you should turn it off for good. I've never seen that.
For people who might have one of these now relatively older SSDs and come here wondering if they should enable this feature, I would recommend you upgrade your SSD instead.