Following up the empty places
The practical use of a roster is what you do with it before you go live. Where a registered name has not been reached by a reminder, or a seat sits unclaimed, the list tells you exactly who to nudge, because every entry is a real person who asked to come. That follow-up is the quiet half of attendance, and it works precisely because the list is trustworthy.
There is no spreadsheet gymnastics the morning of: names, their private links and the running count against capacity have been assembling themselves since the first sign-up. What began as a registration list simply becomes the record of the room.