The staff global group is commonly given to developers who work on MediaWiki and use it for various testing, debugging, or research activities. API limits often make those more annoying (e.g. when exporting pages into a test wiki) so the apihighlimits right should be included in that group. It's one of the most harmless permissions, it's just there to avoid clueless bot users from slowing down the API by doing lots of expensive requests, which presumably is not an issue with people in the Staff group.