Typically brakes are bled when there is air in the system (replace hose, caliper, master cylinder). Bleeding gets the air out. Symptom of air in the system is a soft / spongy feel in pedal.
I am guessing they want to "flush" the brake fluid. Process is same as bleeding, just done more to replace all the fluid. This should be done every 2-3 years as brake fluid absorbs water (which causes several issues).