A few points: - some pegged currencies are still decentralised (e.g. MakerDAO) - they rely solely on smart contracts - even with a centralised peg, you have to trust an organisation to keep the collateral, but the contract can state that anyone can move the funds around, so the managing organisation cannot just remove funds at will Also, compared to a centralised database, you have an interoperability aspect - if it'…
To provide another example besides the ICO: you can use a pegged blockchain-based coin to trade on Uniswap or any other decentralized exchange. This would not work with the database based coin. The idea is not to gain efficiency, the idea is to gain interoperability with the blockchain ecosystem.