I’ve put salt licks out in the past, and very successful they were too in terms of bringing in both roe and muntjac. I have lots of nice trail cam photos showing deer using them. We were using them to attract deer to glades and clearings in the woods, with the intention to shoot the deer on the way to/from the salt licks.
In reality we found we shot very few deer near the salt licks - there was a tendency, unconscious or otherwise, to want to get to a spot near the licks, thereby bumping other deer on the way - and once bTB in muntjac turned up on the ground we stopped using them, for all the reasons
@Buchan has mentioned.
Part of our ground includes a known bTB hotspot. We can never be 100% sure where the deer first picked up bTB, but the blocks put out for the sheep and cattle were certainly a possibility. It was also clear that deliberately putting out something that would encourage deer to concentrate in one area and potentially transfer germs from and between possibly infected deer was simply not worth the risk, however limited that risk might be. With farmers minded to want deer eradicated anyway, why do something that might provoke them?
Of course we also had a large game shoot running on the same ground, so there were already dozens of feeders out there effectively serving prime steak to the deer 24x7, and bTB may well have been spread by the deer using those, which was a discussion I had with the chief vet of the BDS last year. Since the shoot has gone, we’ve not had any recurrence of bTB - though that might well reflect coincidence rather than causation.
If bTB does turn up again - and we all have our fingers crossed that it doesn’t - at least we know that two of the potential means of transmission have already been removed, so can start looking into other things.