In my experience, there are high-end photo labs that will work with you to achieve the best result (and they have in-house technicians with a lot of expertise in preparing your images for printing) - and are very expensive.
Some may even start from your RAW images. AFAIK Salgado never edits on a PC, he has contact sheet printed, then proofs made and then negatives created from digital images and printed (I guess it's not cheap... http://cpn.canon-europe.com/content/interviews/salgado_genesis.do)
Then there are medium-level labs that will print well enough if you prepare the image yourself for their printing device(s) (usually, their technicians will do very little), and low-end labs that expects 8-bit JPEGs in sRGB (or maybe AdobeRGB, in the best cases), which will just print out what they receive. Sometimes the same lab may offer different levels of service, depending on how much you are willingly to pay for a print.
Since prints are made from already processed images, there's very little reason to start from a RAW - which won't contain the required information - most tool working on RAWs like Lightroom stores changes in proprietary formats - which are useful only if using the same applications for creating the print output. How much processing an image requires depends on how you shoot, but very few images usually don't benefit from a little processing.
Then there's the issue of preparing the image for printing. That means tailoring the image to the printing technology and "paper" used. This step - proofing - may be made by the photographer, or by the printing lab.
If you proof yourself, you can optimize the output to match your "vision" - within the limits of the proofing technology. Proofing requires an ICC profile for the target "inks"/"paper" combination - of course, there are technologies that don't use inks (nor paper). When you proof yourself, the file prepared for print will usually contain the destination ICC profile.
Which file formats will be accepted each lab will tell you. Usually high-quality images are printed from TIFF files, not JPEG.
Labs may require the file in a "standard" color space (usually AdobeRGB or sRGB), and will perform the conversion themselves while printing - but of course this lets less room for optimization.
There is also sharpening to take into account. You may want to do it yourself, and ask the lab to avoid any sharpening, or let the lab perform it while printing. Different output technologies - and print resolution/size - may require different types and amount of sharpening, so you need to know it in advance if you perform it.
The more control you have on the printing process - and the higher your skills, the better results can be achieved, but the price can also match it.
) but if you are editing the shots then the raw bears no relation to the final image as adjustments are not made to the raw but stored in a separate file as a recipe of adjustments that need to be done to the raw. I use DxO so I get .dop files for each adjusted image, therefore the raw must be converted on output to a different format. 
