I had been using the canned profile from Ilford for Gold Fibre Silk on my Canon Pro9500 and was finding the prints too dark. Adjusting my monitor calibration and brightness did not help. When I used my ColorMunki Photo to create a custom profile, my prints began looking correct. The canned Ilford profile was very inaccurate for my printer.
I have an Epson 4900 on order and when I have it set up I plan to create a custom profile for it as well. I'm not bothering with the canned profile from Ilford.
I don't know if the canned profile is better than no profile at all, but getting a custom profile is well worth the investment in my opinion, especially considering how much one invests in the printer, ink, and paper, not to mention creating the image in the first place!