From the (NetFlix competition Progress Prize winner) KorBell team's summary paper:
Predictive accuracy is substantially improved when blending multiple predictors. Our experience is that most efforts should be concentrated in deriving substantially different approaches, rather than refining a single technique. Consequently, our solution is an ensemble of many [107] methods.
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We strongly believe that the success of an ensemble approach depends on the ability of its various predictors to expose different, complementing aspects of the data.
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However, in hindsight, we would probably drop many of these results, and recompute some in a different way. We believe that far fewer results are really necessary. For example, based on just three results one can breach the RMSE=0.8800 barrier ... [W]e have found that at most 11 results suffice for achieving a blend with above 8% improvement over Cinematch score.