The checks which the NHS promotes (including the 'poo sticks' for colon cancer) are well researched and targeted to identify specific problems in specific population groups. They are good value for money and good for public health in general.
The 'have a body scan' checks are aimed at making money for the operators - nothing more, nothing less. Yes they may find an occasional problem and even save the odd life here or there - but that is incidental to the main reason for their existence. It probably also has a net negative impact on the population as a whole, as the 'worried well' soak up even more NHS resources chasing imaginary problems flagged up by the scans.