I must admit to passing it on as acquired wisdom too...
However, few thoughts:
1) the acidic tar (which will dissolve aluminium
) must act as an antibacterial coating.
2) It permeates the smokehouse with the smell of mature smoke so some of that presumably gets into the food. It's possible (ie pure speculation) that over time the tar matures and releases new volatiles that you wouldn't find in raw smoke.
3) It gives the smokehouse an authentic traditional look, much more impressive to the layman who wants to see what your smokehouse looks like.
4) It's nasty dirty stuff to have to clean off so any excuse to leave it there has to be a good one
Dave
Curing is not an exact science... So it's not a sin to bin.
Great hams, from little acorns grow...