If you enable the option Continuous saving of email messages then it means that a new email message matching the label or the search filter will be automatically exported and saved into your Google spreadsheet.

For example, if you set up automatical export of the label Leads to the spreadsheet called Spreadsheet with leads, then as soon as you add email to the label Leads the email will be added as a new row spreadsheet called Spreadsheet with leads.

The continuous job can be paused or aborted via dashboard:

automatically save emails