Legal Question in Criminal Law in California

Citation is all that's required

It's not unusual at all. It's a matter of money. The time and resources it takes to arrest a defendant sometimes don't justify the arrest. It isn't necessary to the conviction. Infractions and misdemeanors that are not alternative misdemeanor/felonies ("wobblers") may be initiated either by complaint or by the filing of a citation in the municipal court, per Penal Code §853.6. A citation is all that is required to get you to court to answer to the charges. A report will still be prepared. It's as if you were arrested and then released on your own recognizance (posting no bail). The end result is the same, but the cop is free to make other arrests instead of wasting time booking you. Neverthelss, jail time is quite possible as a sentence on a misdemeanor.

In your case, however, if this is a first arrest, a drug diversion program (PC 1000) or Prop 36 will probably be offered as a way to avoid jail and rehabilitate your record.