Its simple really, on a state level, they are running a deficit, how do you get out of a deficit? increase revenue. decrease spending. Others have argued this will not help rescue (some conveniently decide to omit the word help) the economy.
Whether it be the states budget, or for the overall economic woes it will help both.
State budget, increase in revenue via taxation, decrease in expenditure via enforcement costs. In a nut shell this will help, what legislators do after the fact is moot, although some have attempted to use that as an argument against.
On an overall state economic level, it will help as well. It will create more jobs and revenue within the state in a market that was previously the (illegal) providence of mexican drug cartels and underground production (Mexican cartels have been steadily increasing their position in instate marijuana cultivation in California, illegally, and with illegal labor). The production will go to licensed people who have to submit to a background check, pay a $5,000 initial fee, and $2500 annual renewal. Same fees and background checks are to be applied to retail licenses. The result is jobs and income that has been outsourced and sent directly to Mexico stays in California. These are just the cultivation and distribution aspects and not counting other potential economic bonuses such a tourism, paraphernalia sales, hemp products, ect. In a nutshell billions of dollars of revenue that was sent directly to Mexico stays in California, most assuredly a help for their floundering economy.
This is just the economic impact this could have. A pleasant side effect will be the hamstringing of gangs, and drug distribution related violence, which is epidemic. Will it go away completely? NO, but their cash cow is gone, it has been estimated the Mexican Drug Cartels attain 60 - 70% of their revenue from Marijuana alone. All of this passes through gangs throughout CA prior to eventually making its way to the cartels.
Is this the miracle cure for what ails California?? NO, although some here have been misinterpreting that as the gist of the topic. Will it HELP the economy, both for the states coffers, and for the public at large?? yes.