Ceramic bulbs are a better way of heating snakes that are generally bigger and heavier than say corn snakes.
The best way to look at is a heat mat radiates heat to solid objects, so in theory the heat mat is not heating up the air viv but the object that is directly in contact with.
A large snake sitting on a heat mat will not get the benefit of being heated from above and around it, only the part that is in contact with the mat etc.
A ceramic bulb heats up the air in the viv which in turn warms the snake.
So big snakes = ceramic bulbs
small snakes = heat mats (although you can use ceramics if you wish)
Having said that I used to keep a royal on a heat and had no problems, but if I was going to get another royal i would set ip with a ceramic.
P.S a ceramic needs a different thermostat to a head mat.