What are Webhooks?
"Webhooks allow you to collect information about events as they happen in near real-time. Once you provide a URL and select the type of information that you want to receive, we’ll send that data to you as the events take place."
How does Webhooks work with SyncApps?
When you have a SyncApps integration with Mailchimp, then Webhooks will take effect even if you do not run a sync.
Let's say if you have updated Field A of Record A in your Mailchimp Master List then this will automatically update Field A of Record A in your CRM even if you don't run the sync if you have Update Mailchimp Profile form to CRM feature checked in your integration.