Great answers all around. Here's what I'd add:
* You deliver a product/feature that people actually want
* You position your product in a way that gets the right people to try it (which they then adopt because of pt 1)
* You deliver against whatever higher level objective you’re trying to achieve for your company (increased ACV, capture new market share, increase conversion rate within current market, etc)
BONUS: you learn something you can apply to whatever you launch next
PS note on pt 1: you’re less likely to deliver on this unless you’re working upstream and sharing market insights with your product team. Great product marketing influences roadmap, which leads to great launches.