Sometimes after what seems to be a minor accident, your car, motorbike or van might show no visible signs of damage externally. It might be possible that forces have been exerted on the chassis or structure internally that might not visible to the naked eye, and it is for this reason that it is recommended that you have the vehicle inspected professionally.
There would be nothing worse than shaking hands with the person that hit you and agree there is no damage, only for your vehicle to fail its MOT and become unroadworthy or needing major repair work, with the person that hit you no longer available.