What: A process that moves functions away from a central authority, whereby control is distributed among the participants in a system. In Bitcoin a distributed ledger is shared among participants as opposed to a central authority where the attack surface is much higher. However, because you have a commonly agreed to state, this “decentralized ledger” is “logically centralized”. (R2)
Why: “Decentralization can be a way of improving access to services, tailoring government actions to private needs, and increasing the opportunities for state-society interactions… Accountability is a prerequisite for improved public sector performance, and information is the key to accountability. The systematic collection, analysis, and reporting of information are critical elements of decentralization programs because that information can be used to verify compliance with policy goals, to analyze alternative outcomes, and to guide future decisions.” (R1)
Ref:
https://en.wikipedia.org/wiki/Decentralization
R1: http://www1.worldbank.org/publicsector/decentralization/admin.htm
https://medium.com/@VitalikButerin/the-meaning-of-decentralization-a0c92b76a274