It will tend to turn the beam on when it's off to the side, outside the normal range of the screen. X Windows users in the mid 90s had to put in their exact scanline information or else the screen could blow up. That went away with a combination of multiscan monitors and monitors being able to communicate their preferred settings, but those came pretty late in the CRT era.

Edit: in any case, color screens need to have at least bands of red/green/blue phosphor. At a minimum, there will be breaks along either the horizontal or vertical lines, if not both.