Inspection on your own and even with the help of third party mechanic will not tell you the story on the vehicle.
It also checks to make sure that all working gauges and any direction of drift.
This means that if a wear member as a hose or seal fails and this causes a major engine failure, engine repair will not be covered.
There are many sites that will provide you with things like the invoice price and incentives, and this information can be valuable as you negotiate your price.
The corrosion or rust warranty protects you from the car metal corrosion hassle.
The extent of coverage, benefits and terms of payment are specific to each individual contract.