We have seen some reports that @mouseover is causing some performance issues, please do submit a bug report via the in-game system.
To report a bug inside of WoW, press Esc to open the menu and select the Support button. On the page that opens, below the search box, the second button in says “Submit feedback or bug report”, use this.
If you cannot see the button then this post may help - Trying to raise a bug in-game takes you to US forums - #7 by Chronormi-outland