It's also much safer to reach over to the back of the Flat Top when cooking to prevent burns. There are manufacturing limitations that prevent a tiny lip at the front as some have suggested. It's either a relatively tall sidewall or nothing at all.
It's possible to put 10 pounds of greasy beef in the middle of the Flat Top and walk away and grease would probably run off the front. However, thousands of meals ranging from burgers and bacon to piles of vegetables for fajitas and stir-fry and have been cooked on Flat Tops in our homes and it's never been an issue.
The enormous surface area of the Flat Top allows grease to spread very thin instead of pooling up like it would in a smaller skillet or pan. This prevents the grease from flowing freely around the cooking area.
The front of the Flat Top also develops a very slight bow when heated to make it even more difficult for liquid to flow freely to the front of the Flat Top.
I hope this info helps!