Advantages of decentralized system( block-chain ):
1) No need of central authorities.
2) As this is peer-to-peer network, all of the data is not stored at one place so hacking such a system is impossible.
3) You can’t delete any block of the chain.
4) Reward to be in network.
If the computer is connected to the block-chain then it needs to be connected to internet for 24 hours a day, which requires effort by the individual. So in case of block-chain of bitcoin, some bitcoins are given as a reward to individual computers connected in the network.
5) Penalty on any theft.
If any wrong verification is caught in the chain then the individual is also punished with a plenty.
Disadvantages of decentralized system(block-chain):
1) Takes long time for transaction as the transaction is to be saved in the whole network of computers.
2) Decentralization increases the administration expenses because it requires the employment of trained personnel to accept authority. This results in the increase in cost.