A note in the manual says:
If Show Bars and Beats Positions When Inserting Notes is activated in the Preferences dialog (Scores—Editing page), the bars and beats positions are shown when you click and hold down the mouse button. This allows you to find the correct position.
(Cubase_Pro_Score_12_Score_Layout_and_Printing_en.pdf – WebHelp version)
The text I’ve emphasized (using the strong formatting option) should be replaced with “over the staff”, because the section is about entering notes with the computer keyboard, not with the mouse.
Not complaining. Just saying. 