"...paying digitally make it harder to keep track of how much you’ve spent or charged..."
can't agree with that, digital transactions are much easier for bookkeeping
It depends on the perspective. In the case of Bitcoin, you know exactly how may Bitcoins you sent/received and is to that extent easy to keep track of.
The problem comes from Bitcoin currently being tied to fiat in terms of it's value. As a result, it's much more difficult to keep track of. We know only 21 million coins will ever be created, but a Bitcoin spent now may be worth many more/fewer Bitcoins later on. Even though more coins are being continually generated, a mass acceptance of Bitcoin will make each individual Bitcoin more rare in terms of ownership. The changing exchange rates make keeping track of bookkeeping more difficult because the value of BTC spent is relational. 10 BTC that I sell back in the middle June is quite different than the 10 BTC sent today.
Because of this, if I said, "I spent 100 BTC last year, but I spent 500 this year," it's hard to know exactly what this means in terms of value.