As you gain these you'll get a better chance of capturing related pokemon. Admittedly, training just one seemed illogical since Pokemon guarding gyms are usually high level and high CP (combat power).
Niantic did not mention an ETA for the patch, only that the changes will be implemented in "an upcoming version". According to Niantic Labs, this capture bonus will allow players to catch rare Pokemon easily. Many low level trainers are discouraged from participating in gym battles because majority are defended by Pokemon with huge CP. Important Pokemon types include the Psychic, Gardener and Kindler Pokemons.
However, when Niantic's servers were experiencing server difficulties in the wake of Pokemon Go's overwhelming popularity, the feature was disabled.
Covered by Games Industry, a new report from games data analytical firm Newzoo has shown that there are still over 700,000 people downloading Pokemon Go on a daily basis. Niantic posted a recent update with regards to CP level of the defending Pokemon.
Pokemon with multiple types will give out an average bonus. The game has officially been released in the US, Japan, Australia and New Zealand, but players from other countries are also using different cheats and hacks to install the augmented reality game.
That's pretty incredible, but it's still nothing compared to what Pokemon Go has managed to achieve since launch.
This mechanic was primarily designed for trainers who are stuck in a certain tier as they'll be able to grind their way to the new tier of Pokemon. But it sure that Pokemon Go will release these updates soon in the future.