Health Globe
Health Orbs are globes of life energy that can escape from killing monsters.
Why they Exist

Game Mechanics

The drop rate is quite low, but with the amount of monsters coming at players, there should rarely be a lack of orbs, and when they are far between, there is always potions. Additional tweaks have also been promised.
SourceThat's how it works!
We're also playing around with some alternate functionality for when/how they're picked up while you're at full health, as well as some visual tweaks. Regardless we're going to make sure it's as fun and balanced as possible.
Boss Battles
During Boss Battles, where no extra monsters are killed, individual hits on a boss will have a (low) chance of spawning a Health Orb.
Controversy
There has been some small level of controversy about these Health Orbs as some players do not like the idea of "power-ups" in a RPG game. It is nowhere near the levels of the art controversy, but some people are genuinely upset.
In either way, it is highly unlikely that Blizzard will change Health Orbs significantly at this point.