They do avoid a failure mode associated with seals. I'd think modern seals shouldn't leak that much - they don't - but it's still better to have it eliminated i

They do avoid a failure mode associated with seals. I'd think modern seals shouldn't leak that much - they don't - but it's still better to have it eliminated in design. Full-flow scheme has 2 gas generators - with different fuel:oxidizer ratios, and 2 turbines, each driving one pump of the same propellant which constitutes the main flow through the turbine. Staged combustion has 1 gas generator and (usually) 1 turbine with 2 centripetal pumps, so one of the pumps has the flow of the propellant opposite to the main propellant of the turbine. Here is the danger, if seals don't hold.