For the hobbyist, a RIP like Imageprint (the one that I'm familiar with) can simply life, but isn't a true necessity.
But for someone doing commercial or simply volume printing, especially when a wide variety of papers are used, it almost becomes a necessity. Not having to make custom profiles is a real plus in terms of time and effort.
Some claim the image quality is superior. Certainly in the bad old days it was, though now Epson's drivers are far better than they were. B&W is another area where Imageprint excels.
Not an inexpensive solution, but a good one if you understand its advantages.