Once we've built the product, we can start gathering rich, detailed, tactical data about what is and isn't working.
Building a product tends to involve a bunch of experts making a bunch of assumptions. Now we can test those assumptions and let our users guide our decisions.
Over time, we can optimize the product to eliminate frustrations and maximize delight. We can use KPIs like time on site and conversions to gauge user success. (See Measurement strategy in the Dive phase; it’s payoff time.)
It's impossible to realize 100% of a product's potential out the gate. We use this ongoing phase to eke out every last bit of opportunity and also respond to ongoing changes to your company.