There have been quite a few articles on the benefits. For example the central model would allow the NHS to quickly spot a spike in cases in Town X - a pretty important benefit.
The NHSX app tried to do too much — trying to collect centralised data when one key function didn't need to be centralised was always going to be an issue when trying to get people to install it in large numbers.
Smaller samples are enough for population surveys, while high percentages are needed for the track and trace function. Mixing up the two into one app has doomed this project.