Few photographers have a darkroom these days. The conventional wisdom is to use high volume labs, which have greater economy of scale, saving time and money in the bargain. A division of labor. In practice, the cost of processing medium and large format film is high. Labs are businesses who realize photographers are a captive market; especially those who work in large format.
I'm not all business and happen to enjoy working in a darkroom. It's a pleasure, not a chore, and part of a long tradition in photography. It's also part of the learning process, where every technical detail of the craft is directly controlled by the artist.
Engineers would call this a "feedback loop" because darkroom experience influences the way we visualize subjects in the first place. In the mind's eye, we see the final print--and refine techniques to obtain more useful negatives. The choice of subject, and means of emphasis also benefits from working in a darkroom, as does visual perception.
Apart from practical benefits (refinement of the craft/lower cost), producing a 20x24 print yourself is more satisfying than farming-out the work to somebody else. Beware of the dark side! Artists often discover enjoyment of the craft is more important than money.
Darkroom
In the photo (left) are two Omega large-format enlargers. The enlarger on the left is a 5x7 Omega Chromega "E" dichroic (color) enlarger, suitable for color or black and white prints. This enlarger is still sold, fetching a high price! ($4000) It's a beautiful enlarger, suitable for all the film formats I use. The Omega E has a diffusion head, ideal for color, and many black and white negatives. With a voltage stabilizer, results are also consistent.
The grey/silver enlarger is an Omega Prolab 4x5 Condenser Enlarger. Condenser enlargers are better for some black and white subjects, producing very sharp prints. With a darkroom at home, I plan ahead. If a subject is better suited to a condenser enlarger, I use a 4x5 view camera. Both enlargers will handle a 20x24 print.
In a darkroom we find that medium/large format negatives are much easier to print than 35mm negatives. This explains why so many photographers send the film to a lab. A 35mm darkroom is a completely different experience. I often shoot medium format because it's easier to work with in a darkroom, and fine-grain prints are lovely. With smaller enlargements, we demand less from a negative. Things can get very dicey when trying to print 16x20 from a 35mm shot!
Enlarging Lenses are fairly important. It doesn't make much sense to buy high quality camera lenses, and print with funky enlarger lenses. I use high-end Rodenstock and Schneider enlarging lenses, in five different focal lengths.
In these digital days, high-volume labs are not getting the volume they would like to have! I think a medium/large format darkroom is also a good business idea; one I would recommend to fellow artists. A low-volume lab won't make a million bucks, but it does produce income and cost savings, and can improve our reach as artists.
This section is very general. People write books about setting-up darkrooms, and running them. The heart of a medium/large format darkroom is the enlarger and lenses, but there's a devil in the details. Dozens of accessories, automated processors, film/print dryers, tanks, reels, plumping, temperature control, et cetera--streamline the workflow, and make life easier. My darkroom is functional, but could stand improvement. Fortunately, the checklist is finite, because the room is small!