I've found that several cycles of tightening, loosening and re-tightening bolts that require either copper of dead soft aluminum lead to the bolt to turn in a bit farther than it would with just one cinching up of the bolt. The process has fixed leaks and banjo fittings on my carbs, oil pan leaks and brake caliper banjo fittings.

I assume it is because the washers are a bit hard and cycling them tight and loose a few times allows the crush washer to seat better between the parts.