I feel that police patrols are important for a few reasons.
Crime Prevention
If criminals know that there are police patrolling a certain area, therefore more chance of being caught taking part in a criminal act, then they are a less likely to carry out the crime in the first place.
It also acts as a deterrent to gang activity, which can be a big problem in some areas.
Knowing the neighbourhood
If the police patrol is regular, then the police get to know the people that live there. When they know who the bad people are, then they can make an effort to look out for them, and know when something unusual or suspicious is going on.
Reassurance
I know that I would personally feel safer if I know that there were police patrolling around where I live. It also reassures people that they are doing their job.
Answering calls
The police patrolling an area are often the ones that answer the 911 calls for that neighbourhood. As they are already in the car and nearby, they can usually answer the call much quicker, and be at crime scene faster than they would be if they were back at the station.