I also want to challenge the notion that putting even more people in prison is going to solve these problems. The US has the world's highest incarceration rate. And not just by a little; we're ~5x the UK, ~10x Scandinavia: https://en.wikipedia.org/wiki/List_of_countries_by_incarcera...
We've tried mass incarceration to reduce crime. It does not work. Trying it a bit harder after decades of it not working is not going to suddenly and magically produce a different result.
the "point" would be in part:
1. Actually doing their job. No one can blame police if the DA or a lawyer or a judge fucks up and a "bad guy" walks. We can/will blame them if they refuse to do the job they are paid for.
2. It gets a "bad guy" off the street for 4+ hours. That's 4+ hours where the people police are supposed to be protecting don't have to worry about the criminal.
3. Keeping the record. Even assuming a terrible DA is letting everyone police arrest go free, someday a non-terrible DA is going to come into office and when a case file hits their desk they're going to want to know if the person arrested has been arrested one time or 20 times over the last x number of years. They're going to want to review reports and evidence from those incidents as well.