The following article refers to functionality available in Workflow builder, which is located in:
Administration > HR > Workflows
When a continuous workflow is normally triggered, it will trigger against every matching employee - for example, If you are sending a survey form out to all employee's it will trigger to everyone in the company
However, there may be times when you only want the workflow to trigger once.
Setting up single trigger workflows
When building a continuous workflow, there is now an option called Only trigger once per day - this option will be available to existing and new workflows and by default, will be set to No.
Using the option shown above would mean that each day the workflow would trigger and will only trigger once.
For example if you have a continuous workflow that sends a link to report at the start of the month you may only need that sent to one employee or trigger on that day
The workflow will still have to trigger against an employee so it will trigger against the first employee it finds in the database. So if you have employee's the workflow should trigger for it will only trigger for the first employee.
If you are using this option, you should ensure you are making the Recipient(s) in the workflow steps a individual person rather than a role or send it to an external email address,
For the example with the report - if you put employee's manager in the Recipient(s) field in the workflow step it will trigger the workflow for the first employee it finds manager and no other, but if you use the managers or person name it will always send to them when the workflow triggers.