We built a version that reported two separate numbers — text stored and files stored — and reverted it whole.
Why it was plausible: internally they are different things, stored in different systems with different cost profiles, and the split fell out of the implementation naturally. Reporting them separately felt more informative.
What corrected it: no user ever asked the question the split answered. The only thing anyone needs to know is how close they are to the one wall, and the wall is the sum. The split put an implementation distinction onto the surface, doubled the number of states an error message had to explain, and made "am I nearly full" a question requiring arithmetic.
The general lesson we took: a meter should have as many numbers as the user has decisions. One wall, one number. If you find yourself explaining which of your two meters someone hit, the product is asking the user to hold a model of your storage architecture.