Early in his career the director Rainer Werner Fassbinder visited Werner Herzog to ask him if he would produce his films. Herzog's response was that he should do what he did and produce his own films. So far Herzog has made over 50 films, whilst Fassbinder made 35 features and two television series in his 15 year career.
On average, Ingmar Bergman shot one feature film per year. He would write his script in winter and produce the film in the summer. His model for making films (working with modest budgets, a small dedicated crew, limiting locations) helped create masterpieces such as Persona and Cries and Whispers. His technique of regular production has been copied by Michael Winterbottom who has made 16 features since 1994.
Whilst speed of production does not always yield great films, it can enable the filmmaker to work constantly at his or her craft. Filmmakers such as Hitchcock and Micheal Powell made "quota quickies"(1930's UK low budget features) in their early careers and were adamant that this was a firm grounding for their later features.