Teetime I think measuring outcome is very difficult - are you going to measure 'lives saved' (=deaths postponed), health problems identified, lifestyle changes adopted following advice or what? Or the dreaded 'patient satisfaction'?
And even if you do measure those things, there are so many confounding factors (eg pre-existing conditions like arthritis that might make it difficult to act on advice to take more exercise) that the measurements are probably going to be meaningless.
There are some things which cannot be measured, but it doesn't mean they are not valuable. My results were 'normal' and the effect on me was to make me feel even more determined to take exercise and eat properly, to maintain that normality for as long as I can.
Another benefit might be that it gives someone who perhaps doesn't go to the doctor very often an opportunity to mention something in passing that has been concerning them, but that they didn't want to 'bother the doctor' with, and it might turn out to be significant.
Finally, in a historical context, public health campaigns and measures have been very important. If it weren't for public health, we would still be suffering from cholera and many infectious diseases that have been eradicated through vaccination programmes, venereal disease would go untreated, many more people would still be smoking and people would be unaware of the dangers of too much sun exposure.