Speaking as one who teaches a writing class, the main benefit I think a class provides is:

1. Facilitation -- because many people are afraid to write. They think they need to be perfect from the get-go, or that they must follow a strict set of rules. My goal is to empower people to get out the stories they need to get out.
2. Camaraderie and cross-fertilization -- because different writers use different methods. My students often bounce ideas and discoveries off each other, and they also support each other. Receiving feedback from more than one voice can be a powerful motivator.
3. Tools -- because many people don't know where to begin as far as some of the basic tools are concerned: POV, dialogue, plot and character development, research, marketing, establishing a hook, the uses of metaphor and other forms of word-smithing, resources for basic grammar and syntax, etc.

I've taught courses that are critique-based, non-critique-based, covering general creative writing techniques, and devoted specifically to writing SF. The dynamics differ, but the three areas I've listed are common to all of them.

As for the point made about agents -- yes, they can get you past otherwise closed doors, but they are not required for publication. As of this date, I have never used an agent, though three approached me back in the 80s after my story "Lazuli" was published (Asimov's Nov. '84). I didn't have any novel-length works to give them at the time. (Rather, I did have novel-length works, but they were from my teenage years and I didn't feel they were ready for prime time.) Of the three agents, two have retired from the business and the third does not deal with science fiction.

My publications and acceptances in 2007, all done without an agent, are listed at
hurricanecountry.blogspot.com/200...html

Also, I don't outline per se. I scribble copious notes, talk to myself on paper, draw graphs of character interactions, and go down a lot of blind alleys before I hit upon what works. A friend of mine who also does not do traditional outlines signed her first three book contracts in 2007. I believe she doesn't have an agent, either. What she does have is dogged determination and great time-managing skills.