Documentation matters. Planning matters. For good projects they also tend to go hand-in-hand. Perhaps instead of "a lot of people" you mean a few busy posters? it should also be noted that several case tools and code generators make good use of UML.
But what has learning patterns got to do with planning a project? UML makes good documentation. I don't think its especially useful for planning except for perhaps making a few sketches to make things clearer.
I think you'll find a lot of people here prefer the TDD/only as much planning as needed route over Big Up-front Design.