Well, I might be pretty inexperienced, but in our project management class it was explained pretty clearly that agile (=lots of iteration) works best for projec

Well, I might be pretty inexperienced, but in our project management class it was explained pretty clearly that agile (=lots of iteration) works best for projects with lots of unknowns (especially with a high risk of unknown unknowns), while waterfall (=no iteration) works best for already well-trodden projects in well-known conditions. (We were too busy for an agile class or project, only got waterfall, since it is simpler.)