Bitcoin's use case is not digital cash although Satoshi may have envisioned it to become a form of cash. Bitcoin's greatest value right now is in its being a non-correlated financial asset. That type of assets are useful in the diversification of a portfolio to gain better yields under bearish market conditions. The other major value proposition of Bitcoin is its hardness as money thanks to the fact that its inflation rate is programmed to halve at four-year intervals and that its monetary policy is extremely difficult to change. Bitcoin could replace corruptible central banks and become the new monetary standard as digital gold particularly if boosted by decentralized or centralized second layer solutions that allow the grouping of payments only to be settled at the blockchain level very sparsely. But that is currently theoretical. Bitcoin's adoption is far from that, yet.
Many people fail to appreciate the fact that blockchains are useful for building trustless distributed ledgers that do not rely on trusting any single third party. The distribution, particularly if the consensus mechanism is Proof-of-Work will always come with a high cost in terms of scalability.
In blockchain, the following is true: scalability, security, decentralization, pick two. You can't have all three at the same time. Centralized payment channels work perfectly fine for most applications.