You use a marketing automation platform, such as Marketing Cloud Account Engagement (formerly Pardot), to send out your marketing emails. Even though it's connected to Salesforce, it can be difficult to roll up metrics, like the number of email opens or clicks, onto other objects like Contacts and Accounts. This information would help your Sales and Marketing teams see who is most engaged and should be followed up with.
Rollup Helper works with all objects and relationship types — that includes objects from other Salesforce integrated software, such as Marketing Cloud Account Engagement, and between objects that have a Lookup relationship.
You could roll up information including how many emails a Contact has opened, or maybe fill in a text field that shows the last link they've clicked. You can then use these fields in your reports to inform your revenue team of who has engaged enough to become a sales qualified lead or to make a list of Contacts to put into a new email Campaign.