They're really not as important as you think. They only "clear" about 50% of the murders and violent crimes in the US. For crimes like theft and property damage, they basically don't even bother. They just write a report and tell you to take it up with your insurance company. Less than 15% of property crimes in the US ever see a person arrested for the crime.
Important to note that "clearing" or "closing" a crime only requires arresting someone and recommending prosecution to the District Attorney. They don't even need to make sure it's the right person or make sure the person gets convicted and sent to jail, and they STILL only clear HALF of the murders in the US.
Police sit around on their asses leeching massive amounts of taxpayer dollars, doing next to nothing. We need to take away a lot of their funding and shift it to housing programs and other social support programs, which are what actual reduce crime rates.