I once spent an hour chipping baked-on cheesecake off the inside of my oven. There was a little incident trying to get the cheesecake in the oven that somehow managed to decorate the entire inside. I've had similar problems with casseroles, pies, and any other food that tends to escape the pan. I've even tried spill catchers--as a rule, they block the flow of heat, making for uneven cooking.
That's not the case with the Miles Kimball Non-Stick Oven Spill Catcher, though. The Spill Catcher has a raised center that your dish rests on, keeping heat flowing below it. It catches anything that slips over the edge of the pan or casserole dish and it's a heck of a lot easier to clean than the whole oven. For one thing, the Spill Catcher is non-stick.
The Spill Catcher even works in ovens with heating elements in both the top and bottom--the type of oven I think was made specifically to prevent the use of traditional oven liners, which are designed to sit on the bottom of the oven. And the Spill Catcher is easier to handle than that old standby of a layer of aluminum foil carefully draped on the shelf below a baking dish.