With webhooks, external systems (such as your own back-end or other data providers) can subscribe to Userflow events, and be notified when they happen.
You could, for example, setup your own integration, which gets notified when a user's attributes changes in Userflow, and then synchronizes those changes to your CRM.
Very soon, we'll be be offering Integromat and Zapier apps, which will make integrating Userflow to 100s of other services a breeze. These apps will allow for both watching Userflow users and events, as well as sending data into Userflow.
Webhook subscriptions are currently created via the Userflow REST API. A subscription is configured with a URL, which Userflow should POST to when there are new events, and a list of topics to subscribe to.