Public Intoxication citations on 6th street are like beads at Mardi Gras - they are distributed with reckless abandon. Public drunkeness used to be a crime, and in 1968 the United States Supreme Court affirmed the Travis County conviction for same in Powell v. Texas.
The law has changed, and it is not illegal to simply be intoxicated in public - you must also be a danger to yourself or others to be prosecuted for public intoxication. This is the crux of the defense of PI charges: while there may not be a dispute as to impairment, there is often a significant disagreement as to whether you were in any immediate danger. Many times the police report speculates that you may have fallen down, you could have walked into traffic, or some other possibility that fails to adequately explain how you were in actual danger. Often a person who is a passenger in a car is cited with public intoxication when the driver is arrested even though it would otherwise appear that one is 1) not in public, and 2) not subject to any risk as a passenger.
Finally, the main concerns about public intoxication offenses relate to the public record and what conclusions police and prosecutors might draw if you are ever under suspicion for Driving While Intoxicated. While the citation itself does not expose a person to punishment in jail, an arrest or conviction can be an aggravating factor in assessing punishment for future substance related offenses.