The reason a spatula has holes in them is for grease and other liquid to drain out away from the food when you pick it up.
For example if you're cooking a hamburger and it's greasy the holes in the spatula would allow grease to drip off and out away from the hamburger making it less greasy.
You can also buy spatulas without the holes but the spatulas with the holes have a purpose as in letting the liquid or grease or oils drain away from the food.
Spatulas get their name because of the act of turning the food over with them.
A spatula with holes is sometimes also called a slotted turner.
A spatula without holes is called a solid turner.