2.
Although they have been in use for a long time, there are a number of problems.
Security. If anyone has access to the server with the information, all the data can be added, modified and deleted.
Reliability. If there are a number of requests, the server may crash and no longer respond.
Accessibility. If central storage has problems, you will not be able to get your information unless the issues are resolved. In addition, different users have different needs, but the processes are uniform and can be inconvenient for customers.
Data transfer rate. If the nodes are located in different countries or continents, the connection to the server may become a problem.
Scalability. Centralized networks are difficult to scale because server capacity is limited and traffic can not be infinite.
Decentralized and distributed databases can solve these problems.