In art school they emphasized staying fresh. Experiment a lot, they told us. Don't get in a rut. Constantly try something new. And while it's true that experimentation can bring freshness into an artist's work and help prevent burnout, I've found that experimenting all the time has its down side. Too much experimentation can make it difficult to build a good portfolio of work. Several failures in a row can be hard on one's confidence. Despite all the emphasis in art school on freshness, newness, pushing the envelope, and being wildly creative, I've concluded that repeating a successful formula is a good thing if I'm happy with both the process and the outcome.
Repetition is good to a certain extent. Formula is good to a certain extent. Experimentation is good to a certain extent. It's all a balancing act.