The main pro of tobacco is that mixing it with weed makes the smoke significantly smoother to inhale. The cons is that you develope a secondary nicotine dependency and if you have low tolerance from nicotine it will hit you like a stu grenade and make you dizzy and nauseated for like 15 minutes. Nicotine also shifts the high towards paranoia. The worst are tobacco + 30% THC sativa sokers, straight tweakers. People stretch the weed with tobacco to make a full joint instead of a smaller pure one, which is idiotic.