Cleaner oil is better than dirty oil for any mechanical application so why the question as to why? And the explanation that the filters available at a given time may not be sufficient to clean the oil. It just makes good sense since the big industrial applications usually have secondary or bypass filters from the factory. Enough said.
Bud

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1987 300D Turbo, 175k mi., 1998 BMW 323i Convertible, 1997 F250 4x4 7.3L PSD