If you are updating your website, it is recommended to put your site in maintenance mode. Then, no content can be added via webforms. This would give a problem as the site is not ready to receive this new data.
The disadvantage is that your site can no longer be viewed. This module solves this problem. Your site will remain visible, but no new content can be added.
You put the site in read only mode via the maintenance page.
One can set some exceptions if needed...
Visitors get this message: