What are the medals good for?
NOTE: This answer has been significantly edited with some changes made to Pokemon GO. My original answer is available here, and is still valid for older versions of Pokemon GO (which are no longer playable).
While medals used to confer no benefit to players, this has changed on 0.41.2. Now, type medals (Gardener, Hiker, etc...) will grant a catch bonus for Pokemon of the same type.
For example, if you are trying to catch a Meowth with a Schoolkid medal (Normal Medal), it will be effectively easier to catch that Meowth.
Each rank (gold, silver, bronze) of each type medal will confer a greater bonus than the previous rank:
- Gold Medals (200+ of any given type) will confer an x1.3 bonus to your catch rate.
- Silver Medals (50-199 of any given type) will confer an x1.2 bonus to your catch rate.
- Bronze Medals (10-49 of any given type) will confer an x1.1 bonus to your catch rate.
This bonus is attached to the catch multiplier through multiplication, allowing a noticeable increase in catch rates.
It may also be important to note that if you attempt to catch a dual-type Pokemon, your medal bonus is determined by taking the midpoint (or average) between any applicable medals.
However, non-type medals still have no effect and are just there for cosmetics and the all-important Achievement Get! feeling.
Sources: Vemonus's Answer, Gamepress GUCT
As of Pokémon Go version 1.11.2 for iOS, or version 0.41.2 for Android, medals related to catching 10, 50, or 200 of the same type of Pokémon now give a bonus to your catch rate for all Pokémon of that type. From the patch notes:
Catch Bonus: Trainers can earn a catch bonus for a Pokémon type as they catch more of a specific type.
The details of this change were laid out in a previous post:
We are adding a new feature which grants a catch bonus when you earn medals based on catching certain types of Pokémon (Kindler, Psychic, Gardener, etc.). These new bonuses will give you a better chance of capturing Pokémon with a related type. For example, as you reach a higher tier for the Kindler Medal, your bonus to catch Fire-type Pokémon such as Charmander, Vulpix and Ponyta increases.
The complete mechanics behind this feature are not yet known, as the update has only been live for roughly 24 hours, but the rewards are as follows:
- A bronze badge (caught 10-49 of type X): +1 Catch Rate
- A silver badge (caught 50-199 of type X): +2 Catch Rate
- A gold badge (caught 200+ of type X): +3 Catch Rate
In the case of a Pokémon being a dual-type (Magnemite (Steel/Electric)), you will receive a bonus catch rate equal to the average of your catch rate bonuses for each type. For example, if you have a Bronze Depot Agent (steel) badge and a Silver Rocker (electric) badge, you will get a bonus catch rate of +1.5, as you get +1 from Depot Agent and +2 from Rocker.
These bonuses apply to the following badges:
- Schoolkid (Normal type)
- Blackbelt (Fighting type)
- Bird Keeper (Flying type)
- Punk Girl (Poison type)
- Ruin Maniac (Ground type)
- Hiker (Rock type)
- Bug Catcher (Bug type)
- Hex Maniac (Ghost type)
- Depot Agent (Steel type)
- Kindler (Fire type)
- Swimmer (Water type)
- Gardener (Grass type)
- Rocker (Electric type)
- Psychic (Psychic type)
- Skier (Ice type)
- Dragon Tamer (Dragon type)
- Fairy Tale Girl (Fairy type)
- Delinquent (Dark type)