In the case of Filecoin it’s not space that’s unused for other purposes. It’s space that’s used to store files that users (that are verified clients) of filecoin want to store.
The basic idea of proof-of-stake is that when it comes to validating a new block, one of the users that stake coins gets randomly chosen weighted by the amount of staked coins. That user is then responsible for validating the next block in a way that’s similar to a miner in Bitcoin being responsible for validating the new block when the miner succeeds in solving the computational problem. If a user validates a block that’s invalid they will lose part of the coins that they staked which incentives them to only validate valid blocks.
In the case of Filecoin it’s not space that’s unused for other purposes. It’s space that’s used to store files that users (that are verified clients) of filecoin want to store.
The basic idea of proof-of-stake is that when it comes to validating a new block, one of the users that stake coins gets randomly chosen weighted by the amount of staked coins. That user is then responsible for validating the next block in a way that’s similar to a miner in Bitcoin being responsible for validating the new block when the miner succeeds in solving the computational problem. If a user validates a block that’s invalid they will lose part of the coins that they staked which incentives them to only validate valid blocks.
In practice it’s a bit more complicated then that and for Polkadot explained at https://wiki.polkadot.network/docs/en/learn-staking