This actually has really annoyed me. On the odd occasion that I'll think to myself "I fancy some Chesterfield Blues" (I prefer them to Reds) instead of buying baccy, I now can't see if they actually have any Chesterfields there. So then the clerk has to take the time to open the screen, look for said cigarette carton, close the screen, and get back to me all whilst there's a cue forming behind me. Which doesn't do much for my social anxiety.
If there was no screen, all of that would become irrelevant if they don't have any in.
It also means I have to queue up just to ask them if they have the brand I'm after, which turns out to be a waste of my time if they don't.
As I said. Annoying.