I cash out crypto for fiat regularly -- so I always measure my holdings in fiat value. It's always nice to remember that you haven't made any profit until you cash out. Crypto profits are imaginary until you see fiat in the bank account.
But what about when we will be able to pay almost everything with crypto soon? Then you have vashed out the moment you converted to BTC, LTC, ETH or other accepted currency? How will we measure then?
We are still very far from the day when will will be able "to pay almost everything with crypto". That would require a huge crypto acceptance and some kind of stable crypto/fiat pairing. That implies heavy crypto regulations. And that is not yet on the horizon...