For the longest time, the Medals you earn as you play Pokemon GO had no real value. Before the Gym System was totally revamped and you could then earn Gym Badges, Medals were all players had to show for their accomplishments. Niantic later made the Type Specific Medals help players increase the odds of catching that given typing of Pokemon, where the higher medal you had would further increase the capture rate. However, this continued to leave the other Medals that had nothing to do with capturing a certain Pokemon with zero value whatsoever.
Now, however, Niantic has begun releasing Clothing Items that can only be unlocked in the Pokemon GO Shop when you earn Gold Medal for these given category. If you earn a Gold with the Magikarp Medal, you will unlock the fisherman outfit. If you earn Gold with the Battle Girl Medal, you will unlock a workout outfit. And if you earn Gold with the Jogger Medal, you will unlock the jogger outfit. After being unlocked, all of these outfits can then be purchased from the shop in exchange for coins. More of these outfits, the same that emulate NPCs from the Mainstream Pokemon Series, are also expect to come.