After they're signed up/subscribed, you send an "onboarding" email with general information on how to get started using the service, and encouraging them to do things that affect whatever KPIs your boss cares about.

They can be genuinely helpful for tools that have a steep learning curve, either by serving as an entry point into the documentation or by providing contact information for support.

Otherwise, at best they serve as a reminder in case you get distracted before you finish setting up your account.