In dealing with larger systems - one of the biggest plusses I’ve been able to identify is that when a customer receives a statement they can click on any invoice in the statement and they can download the invoice being referred to.
Obviously there’s a chance of information leaks here that would need to be dealt with - customer gets a username/password to access the system or something
The idea here is to get the customer to manage their own documents and lighten the load of the accounts admin people