According to taginfo, there are over 27,000 nodes bearing this tag, most of them in Spain:
note=If you change this node, please, report to nomenclatorign at gmail dot com. Thank you.
https://taginfo.openstreetmap.org/tags/?key=note&value=If%20you%20change%20this%20node%2C%20please%2C%20report%20to%20nomenclatorign%20at%20gmail%20dot%20com.%20Thank%20you.#map
Overpass query to find them: http://overpass-turbo.eu/s/k5e
It does not seem to add any information at all, because, who in their right minds would send an e-mail after editing one of these nodes, assuming it is even noticed or viewable by the editing client. Keeping up with map changes is a user’s own business, and other editors shouldn’t have to worry about this.
From the quick check I did, it seems like all of these were added by user:egrn or user:Osmand+
I would propose these tags to be removed, as they pollute the database and also make personal information public (imagine everyone doing this, making typos in e-mail addresses etc.)