A major benefit I see is not throwing people in jail and ruining their lives for something as relatively harmless as smoking weed, as well as not wasting 20 billion dollars of tax payer money per year to do so.
If the consequences of the law are far more dangerous than the reason the law was made, it's shitty, unjust, oppressive, and a complete waste of time and resources. Add that to the fact that it's an incredibly ineffective law at what it's trying to accomplish, and that law is complete shit.
Though come to think of it, marijuana wasn't even criminalized in the US due to concern for peoples well being. It was criminalized so the US government could throw Mexicans out of the country during the Great Depression. Even the creation of that law was completely and utterly ****ed up and built around oppression and lies.
The criminalization of marijuana is only maintained through completely deceitful propaganda (For example: In middle school gym, we were required to watch an anti-drug PSA that said "just one hit of marijuana can kill you"😉, an unfair social stigma built upon that propaganda, ignorance also due to said propaganda, and lobbyists who oppose legalization on the grounds of money rather than morality or concern for health (the biggest lobbyists against marijuana being Alcohol, Tobacco, and Pharmaceutical companies).
So really, the criminalization of marijuana only exists because of certain people's agendas that are completely unconcerned with morality or health, getting much of its support through ignorance propaganda and lobbying, and only serving to oppress people, waste government resources, and creating far more problems than it solved (if it really solved any problems to begin with).
And that is why I believe criminalization of marijuana is a completely ****ed up thing that should not exist in modern times. Unfortunately it does however, so props to Oregon's state government for discontinuing that bullshit in their state. 👆