ARPPU measures the depth of spending among payers, separately from how many users pay. Paired with payer conversion, it explains IAP revenue: IAP ARPU = payer conversion × ARPPU.
Because spending in games is heavily skewed, ARPPU is sensitive to a small number of high spenders. A single large purchase can move it materially in a small cohort, so look at the distribution (median, percentiles) as well as the mean.
When ARPPU rises while conversion falls, you may be monetizing a narrower, deeper base — a trade-off worth making deliberately rather than by accident.