RAID cards CAN help with a few things ...
(1) If the controller is "TRUE HARDWARE RAID", then it will take the load off of the CPU, because native RAID is software based.
*** A THG Team member informs me that this is no longer such a big deal as it used to be.
(2) Allows you to go external ... taking load off the system PSU (especially for LARGER RAIDS).
(3) A 4x Slot-based SSD can totally saturate (exceed by far) the 6Gbit SATA3 interface bandwidth and, so, NEEDS a 4x or 8x slot.
Yes ... Eye-Finity can run 3 mons on one discreet GPU card ... BUT ... It should be (at least) a 5850 (or higher) and you will need to purchase an "Active Display-Port Adapter", at a cost of ~$100, to run the third mon ...
... SOME monitors have a display-port interface built in, and I am fairly certain that, with those monitors, you can forego the active DP adapter.
And ... when it comes to enterprise requirements, with specialized performance monitoring and alarms and controlled shut-down and continuous archiving and scheduled events and emergency swapping and general compatibility with storage server arrays (rows of racks) ... well, you get it ... your avg. desktop mobo buyer does not want to pay for all that. ... They want to edit dense codecs, etc., and the integrated solutions have a fixed number legal configs.
These days ... for us normBal folks ... Integrated RAID id purdy darned good and the CPU can do that (too), without breakin' a sweat.
. .. If you don't have a clear reason to go external ... then don't.
(prolly cheaper to upgrade your PSU and a few fans ... even a bigger case).