Well my opinion is that it gets you more familiar with the underworld since it's illegal (atleast in my country) since if you find way to buy weed you will be able to find coke or any kind of pills lateron. Also you get familiar of getting "high". Before you got high the first time, the idea of smoking weed and getting high was taboo, SO snorting coke or injecting heroin would be a hell no for you. But when weed replaces tobacco(atleast in my experience) or becomes a habit and not a big deal, next step would be taking LSD/MDMA and so on.