Baked-on food looks gross, smells gross, and can mess with the flavor of your food. If you've got a fume-free and non-caustic oven cleaner, just spray, close the door for two hours, then wipe clean with a warm, damp cloth. Finally, run the oven at 300 degrees for 15 minutes to get rid of any remaining smoke or fumes.
If you've got any other kind of oven cleaner be really freakin' careful because the fumes can be dangerous for your lungs, skin, and oven. You'll need to open the windows and wear gloves, a dust mask, and a top with long sleeves. And make sure that your oven isn't self-cleaning, because this stuff could destroy the surfaces.
Get Easy-Off Professional Fume Free Max Oven Cleaner from Amazon for $5.97. (That's what was used in the photos above!)