Disintermediation is where real value lay, decentralization is just a method of handling the lack of an intermediary. However in a sense a block-chain is an intermediary itself, so where we see crypto projects removing a centralized intermediary and replacing it with a decentralized intermediary, this does very little to add value or reduce the costs in a system or process.
The reason the currency application of block-chain works so incredibly well, is that banking has so many intermediaries; if I want to send you money, I have to ask my bank to send your bank some money, so we already have 2 intermediaries involved. If those banks dont have accounts with one-another, they may use a 3rd correspondant bank to execute the transaction. That is for a simple domestic transfer, now if we need to add an international dimension, the number of intermediaries starts to explode, fx brokers, central banks multiple correspondant banks and so forth; every intermediary needs paying, is slow, error prone and able to be corrupted.

Other useful scenarios are supply-chain, energy-supply and any other application where multiple intermediaries are blocking efficient processes.