This used to be a glitch in the game I'm currently playing (PokeClicker), but it's since been patched as part of the game's Quests instead.

Basically, whenever I had a Qeust that involved catching a certain number of Pokemon or catching a certain number of specific Types of Pokemon, hatching Pokemon would be counted as catching them. It was a great way to save in-game currency and time on catching wild Pokemon, but as stated before, it's become part of the game's Quests instead.