In rare instances it adds a bit more character to the actor's performance. I'd cite the late John Savident's excellent portrayal as Fred Elliott, I say Fred Elliott in Coronation Street. Later as the writers struggled to give him meaningful scenes he'd be leant across the bar, give a funny noise and deliver his one or two sparingly given lines and tap his cigeratte on the bar somehow making it more meaningful.
There was one play I've been in where I was required to smoke in back at uni called Look Back in Anger by John Osbourne featuring the original 'angry young man' Jimmy Porter. I played his amiable Welsh flatmate Cliff and was needed to smoke like a chimney. Having never smoken before or since I was reluctant to do so for obvious reasons and reached the compromise that I would have a real cigarette and just hold it a fraction away from my mouth and not inhale rather than use a fake one. Great play tho with wonderful dialogue and some truly great performers to be alongside in Preston Drama Club. Later I found this is the same company where the wonderful Leonard Rossiter started out in rep.