Removing any air pockets that may be in the lines. Really only necessary if you have fairly old brake fluid or if air was introduced into the lines during the brake job.

1999 Red / Tan SVT #1969 of 2760 Built 4/21/99 K&N, DMD, FMS Wires, ES Insert / Bushings, PF End Links 17" FSVT 5-Spokes Factory Spoiler 35% Tint All Around