There are two advantages of PoS consensus algorithm. First it is more energy efficient and environment friendly than PoW, which requires the use of heavy computational resources like mining rigs. Thus it helps to save cost in electricity and buying the quipments.
Secondly it secures the blockchain against 51% attack. To halt the blockchain, you need to own at least 51% of the entire coin, which is very unrealistic and impossible. As the size of the users and their stake increases in the blockchain, the chance of malicious attacker trying to purchase 51% of the entire supply to attack the network is highly unlikely. Even if they attack, it is likely that the cryptocurrency value would fall and the money the attacker invested would have low value afterwards.