If you never clean your oven, dirt will build up and affect how it works. Excess grime can block the air vents and damage other mechanical parts. This will lead to irregular temperatures and unpredictable cooking, increasing the chance of food poisoning. Sometimes the damage can even result in having to book an engineer to repair your oven.
You should also be aware that loose bits of burnt food can cause your oven to smoke when in use. Not only will this leave your meals tasting terrible, but if spilt grease is left unchecked, grease fires are also a possibility. We've got everything you need to know if you're dealing with a smoking oven.
A lot can go wrong, but if you keep your oven clean, you won't have to worry about any of these issues.