The effects of Marijuana will change according to state. THere are many factors, including the economy, crime rates, ETC. Marijuana is a controversial decision, yet is won't have a large enough impact on the nation for it to have to be a national decision. If this was up to the federal government, it would take up even more precious time to try and get the entire nation to agree on one decision.
The states should decide whether or not to allow marijuana, despite it having many medical benefits, and few harms. This allows people to be better able to compare what works with what doesn't, and more to states with better ideas and policies. Also, this question is poorly worded, and may result in confusion.