Using the downvote tool is how you use your stake to remove rewards from a post (or a comment). The rewards “go back to the pool”. Technically, there are always a number of posts that are less than a week old. Those posts are called “active” posts. What Hive users do is upvote or downvote on them to collectively determine the Reward Shares each of those active posts will get. Whenever a post reaches the ripe old age of exactly one week, the Hive blockchain code calculates the proportion of the available reward pool that the post will get.
Why does it exist? Fundamentally, it exists because Proof-of-Brain is all about stakeholders expressing their opinions about the value of each piece of content. Stakeholders need a tool with which to remove rewards from spam and scam content, worthless content posted only to farm votes (a practice colloquially known as reward pool rape), or simply to remove rewards from content they find over-rewarded. In PoB, stakeholders are the guardians of a common resource: the reward pool. As investors, they must have the necessary tools to protect the value of their investment, which is what they get in return for the tokens distributed to the content creators and curators.
The Hive blockchain can be accessed using many different front ends including but not limited to:
For more info on HIVE: Hive - The Blockchain & Cryptocurrency for Web 3.0
Join the HIVE Quora Space: The Hive