We log a \core\event\webservice_function_called event every time a ws is called, the more JS-based UIs we have the more events we have, same for requests from the mobile app. Those events already represent a 2-digits percent of the standard log store table in some cases.
This event was added in
MDL-21127 (2010) and it does not even seem related to the issue's main purpose. People might be using it (incorrectly) to observe calls to ws functions. I don't know if the events2 API would allow events to be observed but not stored by the log stores layer. If it does not I would vote for just removing the event.
Juan Leyva proposed to add a setting to opt-out. A possible problem of the opt-out approach is that a sys admin may not know if any of the 3rd party plugins they installed is observing this event, so they would not know if they should keep the setting enabled. I may be ignoring other uses of the event.
In any case we should ask the community about this.