I had a report done by the RAC before I bought my car a few months ago. It highlighted quite a few, mostly minor, things whilst missing others completely (e.g. the bonnet wouldn't open...until I found the relevant thread on this forum, which explained that it was a common problem and what to do to overcome it).
The report produced a list of minor faults which I discussed with the Dealer. His response was 'No problem at all, we will put all of these right for you'. The problem was that we had no real way of checking whether the faults had actually been put right and, short of paying for a second inspection, how could we know? I suspect he put few, if any, of them right.
So, for me, the report was useful in terms of reassuring me that there was nothing catastrophic wrong with the car (I think it would have spotted a lemon) but it definitely had limitations without some sort of follow up.
With hindsight, some written inventory of the work carried out on the car, or some sort of 'sign off' from the dealer, would have given me more confidence that everything had been put right.