Care and Caution
Be careful when using a griddle, especially a cast iron griddle, on ceramic smooth top stoves. Griddles can scratch the surface or even worse, cause a glass stovetop to crack. Don't slide a griddle across a smooth top stove. It can scratch the ceramic surface. Always lift a griddle rather than slide it. Use two hands for more support if needed. Never store a griddle above your stove. Accidents do happen and griddles are very heavy. If dropped on the glass stovetop, it will crack its ceramic surface.
Know the Condition of your Griddle
Check the underside of your griddle. Many griddles have a smooth cooking surface with a ridged undersurface. This ridging can pose problems when cooking foods that might release water or juices or if food spillage occurs and gets trapped between the ridges. Steam can build up between the ridges, and the slight difference in surface temperatures between the ridges might crack a glass top stove.
Check the condition of your griddle from time to time. Place the griddle on your smooth top stove so that it sits flat on the stove surface. Over time, a griddle can warp and become slightly wobbly. While this won't affect your ability to use the griddle, an off-balanced griddle increases the risk of runoff from liquids, which can crack your stove. Consider buying a replacement griddle that sits flat for safety's sake as well as to control foods cooking on the griddle surface to prevent spillage.
Risks You Should Know
Placing a large griddle over two burners will allow you to use the griddle's total cooking surface. However, you run the risk of creating a differential in surface heat temperature between the two hot burners and the cooler space between them that's not sitting directly on a burner. This situation could cause the glass to crack.