Short answer
HubSpot's KB: simple workflows in marketing emails can, for example, add contacts to a segment after a click. Actions include delays, more emails, internal notifications and tasks. Copying an email can include its simple workflows. More than one simple workflow needs Professional or Enterprise.
1. In HubSpot
The relevant screen in my demo portal.
2. Worth knowing
One-to-one sales follow-up belongs in sequences instead.
3. Related
Email health and automated emails.