People that use tobacco have significantly lower rates of Parkinson’s than others. There are some indications that this may also be true for cannabis. Both substances may also help prevent Alzheimer’s and Dementia with Lewy Bodies.
Both drugs, obviously, affect the brain and are enjoyed by many people for their immediate effects. It is possible that users of these drugs to some extent are using them because they really do some good, both short and long term.
For different but similar reasons, it is plausible that people who crave opioids, methamphetamines, psychedelics, caffeine, and other drugs are doing much the same.
I hope we will see more science on these and other popular drugs from now on. A great deal of biochemistry is shared among plants and animals. We have all evolved together.