Depends a lot on degree and nature of Flat Feet.  Studies have shown people with flat feet are 50% more likely to have osteoarthritis. Also postural problems have been found linked to flat feet.

The chain reaction starts with a fallen arch causing inward twist to the ankle, shin and knee, in a corkscrew motion putting stress on the hip and pelvic joints. Then the spine will tilt and the back muscles will strive towards correcting an upright posture

Flat feet and posture problems, disadvantage of flat feet