As a prosecutor for the Department of Justice I don't really feel that it's my place to take a position on this bill. I will, however, make a few comments about what I think this would do to enforcement:
I'm not sure how much this bill, if passed, would change enforcement. First of all it would not affect the states -- by far the biggest source of criminal arrests and prosecutions. I don't have stats, but I would be very surprised if there are many federal prosecutions of people possessing 100 or fewer grams of marijuana. Second, even at the state level, this would only affect arrests and prosecutions for small quantities of marijuana. In many jurisdictions, such crime may not trigger an arrest or a prosecution. It may be dismissed or it may be sent to a pretrial diversion program.
Also, it is a little misleading to say that possession of marijuana consumes such a large percentage of our resources. Simple possession of an amount like this is rarely the subject of serious investigation. Instead, it's the kind of crime that's charged when officers are doing drug interdiction (for example: scoping out an area and arresting drug sellers), when they stop a person or vehicle, get consent to search, and happen to find marijuana, or when they are conducting a search or investigation that happens to turn up pot. If you're trying to stop street-level drug sales, this law won't change anything: distribution is still a crime, and you often can't tell at the time of the sale whether the person is selling pot or coke. Similarly, an officer isn't going to stop asking for consent to search or cease making traffic stops: such enforcement techniques could yield harder drugs or weapons.
Also, 100 grams of marijuana is a quantity large enough to be consistent with distribution or intent to distribute (depending on other factors, including the packaging). You might have 100 grams that you keep at home as a supply, but if you're carrying 100 grams on your person, you may not be just a user.
Finally, legalizing marijuana may have positive effects, but it would be naive to think that would solve much with street crime and street-level drug use. If we legalize pot, we don't provide jobs to the dealers nor do we necessarily provide resources to the addicts. It's possible that, ironically, the largest benefit would accrue to the group that it would seem the legislation is least trying to protect: recreational users who are otherwise economically and socially stable. But that's just a theory, and I don't have much to back that up.
