As per open ledger and privacy concerns:
One of the points often made is being able to find patterns in a users transactions and comparing them to user patterns. They could then compare them to figure out the identity of the user. I was always intrigued by the concept used for Z Cash.
I never invested in it but the idea is interesting. The issues come when verifying transactions. There is much more computations involved so it is a more difficult process. There is a great podcast on how they came up with the unique encryption code to ensure it wasn't hacked. You can check it out on radiolab HERE
The idea is that the transaction would be more like using cash. Very hard to trace.
