This is the answer to the HubSpot question about what happens to an email if it's skipped due to a send frequency setting.
If a send frequency limit is enabled for marketing emails, and an email from a workflow is triggered, that's more than the daily allotted amount; it will just get skipped. It will not go the next day when the send allotment opens up again.
If the contact is in a workflow and still has additional steps that include emails being sent, they'll receive the next email in the workflow, as long as on that day, the send frequency has not been hit.