Here's a good example of why we do this.
A pony with long term chronic laminitis had blood taken for ACTH and insulin tests in mid-August. 2 weeks later the owner spoke to the vet and was told that the pony didn't have PPID, the insulin result wasn't given. TLS advised that the owner should obtain the actual results, not an interpretation of the results.
Several days later the vet advised of the insulin result, which was well over 100 uIU/ml - a large increase on an insulin test carried out at much the same time last year. The pony's diet, management and foot care were improved on the previous year (when the pony tested negative for PPID) - something had to have worsened.
The following day the lab's results arrived in the post - the pony had an ACTH of 107 pg/ml, the lab was using Liphook's reference range of <47 for Aug to Oct - we know the blood wasn't frozen without being centrifuged, and the pony wasn't ill, wasn't in pain or stressed, hadn't been exercised - there seemed no reason for the high ACTH other than a pretty definitive diagnosis of PPID (plus mild clinical signs - increased hairs on jaw, neck, back of legs, muscle loss, weight loss, fat pads, worsening laminitis in the autumn...).
The pony will soon start on Prascend, and hopefully treatment for his PPID along with a low sugar/starch diet and good management will help to lower his insulin levels. But what would have happened if the owner hadn't asked to see the results - would the pony have been assumed by all to not have PPID? Would another year or more have gone by with worsening symptoms, uncontrolled laminitis, a suffering pony and owners tearing their hair out in frustration at not being able to help their pony?
Looking after a horse with laminitis needs to be a team effort - owner, vet and farrier/trimmer all have an important role to play - for that to be effective, there must be good communication between all parties. We know of at least one owner who changed vets because they wouldn't provide copies of test results....