A lot of people in the US still don't believe Russians interfered in the election, and/or that they interfered to support Trump's candidacy. I believe this is mostly designed to show them (1) yes, they were doing a lot, and (2) it was aimed at disparaging Clinton and supporting Trump.
Similarly, the US government hasn't really taken any steps to prevent future meddling in US elections. The goal may have also been to serve as a wake up call to our elected officials to take this issue seriously.
The indictment is not about PR, it is about punishing Russian nationals who participated in this op.
The long arm of US law enforcement may not be able to get these folks in Russia, but it can prevent them from traveling in many countries around the world, and can result in their assets being frozen.
The other thing is that if any of the individuals involved come to fear for their safety from Putin's government, these indictments will be a strong motivator for them to rat other parts of the Russian intelligence apparatus.
Similarly, the US government hasn't really taken any steps to prevent future meddling in US elections. The goal may have also been to serve as a wake up call to our elected officials to take this issue seriously.