Since it is a windows service, RST will speed up access to certain files while in windows, also monitors the raid array and will warn if something is not right with the array. The service does not do anything until windows is fully loaded. I don't think it has much to do with the newest Smart Response Technology which was designed for use with SSD drives as cache for spinning hard drives.
From the Intel website half way down this page, RST performs several functions.
"With additional hard drives added, Intel® RST provides quicker access to digital photo, video, and data files on single-drive or multi-drive systems with RAID 0, 5, and 10, and greater data protection against a hard disk drive failure with RAID 1, 5, and 10. Support for external SATA (eSATA) enables the full SATA interface speed outside the chassis, up to 3 Gb/s."
It is also hard to tell just how much of this RST or SRT technology is embedded in the Intel chipset firmware, if it is in the firmware (guaranteed it has to be in some form), then it is active and functioning as soon as the bios completes post, long before windows begins to load.
One could assume this newest SRT Technology has taken over part or all of the RST function when it comes to making file access quicker, finding specific technical documentation is near impossible due to the fact that most of it may be considered a trade secret.
My Conclusion, the RST Windows Service is only one small part of the entire technology.