This is a good high level summary of round pen use. Unfortunately some people are not aware of the subtle responses a horse gives or how their action create other reactions both good and bad.
I agree with you, Galadriel, it would be nice to have a round pen, just for working with the horses. I try to work in the pasture, but it works best when the other horses are not around.
Many times training pens offer an opportunity to work with your horse, gain their trust, and give them an opportunity to learn new skills outside the saddle— resulting in increased rider safety.