I have found a big difference between smoking cigarettes & smoking weed. Cigarettes, not so problematic. Weed? Really noticeable. I can usually hear the effects more in someones laugh than anywhere else. Especially when it's a deep chested laugh.
Most of the singers I know who smoke--including one opera singer who has been a soloist for 50 years--actually only smoke a couple of cigarettes every day.
I'm not sure even that is a good idea, but they aren't SMOKERS (like I was for 40 years).
GavestonPS, I worked at a major US opera house for close to a decade, and unless something's changed, smoking is actually quite common among opera singers. I could rattle off the names of a dozen or more soloists who are or were smokers. That said, I've been out of the opera game for a few years now; smoking might not be as common as it once was these days. And it's probably worth noting that many of the performers I worked with who smoked were European, and smoking has remained more common and accepted in many European countries while it's become more derided in America.
That said, I'm really struggling to understand why so many people seem to care who smokes and who doesn't. (And this is purely speculation, but I imagine Miss Minnelli's vocal decline is related more to alcohol than smoking, as alcohol is far worse for the voice.)