What is the point of a blockchain with an anonymous currency?

[ulhaq]

Many anonymous currencies have blockchains - eg, PIVX to name one. But what useful information can it provide? Eg, no one knows how much currency went from one public address to another public address even using the blockchain.

And does it solve the problem of blockchain bloat? In other words, if the history of the blockchain is not needed, it can be pruned at some point?