The problem lighting and ecash are both trying to solve is how to scale bitcoin such that everyone can use bitcoin. Lightning has scaled bitcoin to allow for more transactions and works great now and anybody that want to use it can and in a self custodial. The problem is that most people think eventually not everyone will be able to use lightning in a non custodial way. This is because there is a limit of how many utxos there are and a utxo is needed to open a lightning channel. Ecash wallets like cashu and fedimint try to solve this problem with the tradeoff that the users of the mints do not have complete control over the funds anymore.

It is a improvement for lightning custodial users. Instead of a account you get real ecash that is pegged to satoshi. The mint can not censor a specific user or identify where your payments flow if a lot of people use it. But the mint can print more than it has like banks do. Ecash is not for hodling, it is for fast anonymous payments.