ASC-606 and IFRS-15, the standards currently mandated in the US and Europe, states that revenue should be recognized only when performance obligations are met. For a subscription business, this can get challenging when you account for mid-cycle upgrades, downgrades, cancellations, and the refunds or discounts attributed to it.
When done right, revenue recognition in accordance with ASC-606 and IFRS-15 can help you improve revenue predictability, and converge on your true valuation.