A flat grate is a single-panel grate that replaces the rotating sandwich grate. The “sandwich” grate that comes with every chicken cooker has a set distance between the two panels, and some foods are either too thin or too thick to put in the sandwich grate. Besides, when you’re cooking items, such as steaks or burgers, you will probably want the fire closer to the food, so you will raise the charcoal pan and set it on the charcoal pan brackets (custom upgrade on some of the units). With the pan raised, you can no longer flip the standard sandwich grate.
This is where the flat grate comes in. On the BBQ26S and BBQ42 you can get by without a flat grate when you hook the top part of the sandwich grate onto the open lid. But even then, the flat grate is a little handier and you’re able to close the lid when you’re cooking to control your fire in case of flare-ups and capture some smoke.