When a user makes a change to a Gliffy diagram there is no option to make it a "minor change", hence many notifications are sent out to those watching the page.

A workaround is to remove the Gliffy markup by a minor change, then reinsert it, making the desired changes and saving the page. This sends out much less notifications, but still produces some.

https://support.atlassian.com/browse/JST-18319 is an example of a request for this.