I first saw this tip from a B&M instruction set.
Improves fluid flow to the front clutch pack, for better lubrication and cooling in lower gears.

Rear_piston_retainer1_enlarge.jpg
1993 Daytona, 5.50 at 130mph (1/8) 1.19 sixty ft (PG). Link to 572 B1 - Part 1