Why? To maintain the pressures differential between fuel pressure and manifold pressure
How? Boost pressure is applied to the diaphragm in the fuel regulator,which increases effective spring rate.
Keeping the flywheel/in plate/pressure plate and both frictions relationship the same prevents any issue with run out in the clutch or the possibility of alinging two high posts with each other and causing drag.
One is a highly toxic carcinogenic liquid that is harmful to waterways and aquatic life. The other ensures consistent limited slip differential operation.