Before Guliani, people would say "don't worry about 'minor' things like teens breaking windows, drinking and pissing in public, selling a little pot here and there and stripping idle cars and putting them up on cinder blocks, etc., etc.
"After all," the jaded city people of New York City would say, "We have more important crimes for our police people to address."
But Guliani did not subscribe to that nonsense. He correctly realized that is is the little crimes that lead to the bigger crimes. Once a particular neighborhood was allowed to have boarded up windows, cars up on blocks and kids selling dope, then more serious crime would quickly follow and that neighborhood would become unliveable for decent people.
So Guiliani had his 40,000+ people focus on petty crime. Drunks and bums were rousted out of streets and hallways of public buildings. Broken windows got quickly fixed and graffiti got immediately painted over while vandals got arrested. Abandoned cars were immediately towed away. Trash got picked up. Police stopped "windshield washers" and took them off the NYC streets. Jails filled up and the streets got a lot safer.
We need that same mentality everywhere. People might yip and yap about some 17-year-old kid getting 2 years of jail time for selling a little pot. But guess what? This kid is no longer selling pot and chances are he will not do so when he gets out. Chances are that many other 17-year-old kids like him are selling pot no more.
So we make an example of this 17-year-old kid in order that our streets be a little safer and that others like him are discouraged from making the same mistake.
Crime was reduced pretty much everywhere in the 90's, not just NYC.
Two years is pretty steep. A bunch of students at our local high school were busted for making bomb threats and putting what turned out to be a fake "device" on the roof of the school building. Just one of those students was sent to jail... for two years.