The reason there's a hole in a wooden spatula is to keep you from over beating the ingredients which allow for better sauces and cakes.
The hole in the wooden spatula also allows the liquids to pass through when you're trying to lift something solid.
A wooden spatula with a hole is also good for fluffing rice and grains and keeping chunks in chunky sauces as well as preventing over beating, reducing weight and collecting ingredients.
Solid spatulas have a flat flipping portion that doesn't include slots or holes.
This means there aren't any openings for food or batter to fall through.
For this reason, solid spatulas are perfect for flipping pancakes, sandwiches, and other food that could crumble up or lose pieces when flipped.
Solid spatulas are best when you don't need liquid to pass through and spatulas with holes are best when you need liquids to pass through.