Umm,Atamasama, this forum is for factual answers. You should know at least something about a subject before answering.
In a modern society, an unemployed pool is seen as being both inevitable and indispensible. The unemployed pool is what gives the labour market flexibility. If everyone were employed, then the only way that an employer could get another worker would be to offer more money than that worker’s current employer, leading to rapidly spiralling wages, massive inflation and a level of uncertainty that would make offering most services impractical.
In a system with 100% employment, which you claim is optimal, what happens when the local hospital needs to open a new wing? To employ a janitor, the hospital needs to offer more money than the local fast food restaurant is offering, In fact, because janitor is less desirable work, they will need to offer substantially more more. So if McDonalds is offering $10 an hour, the hospital will need to offer $15. But McDonald’s isn’t going to go short staffed, so we rapidly see a bidding war between the hospital and McDonalds for a 25 year old with no education or skills.
That will repeat for every single job in the country, and the result will be ever-increasing costs for health care and food, as well as every other commodity in the country.
Then we have the problem that nobody will invest in a factory if they know that wages are spiralling upwards and they can’t guarantee that their entire workforce won’t be wooed away next week by higher wages offered by a competitor.
0% unemployment means that labour has become limiting on economic growth. That’s not a good thing for anybody. Like every other essential commodity, their needs to be a surplus to keep the price affordable. No surplus and the commodity becomes a luxury item that only the wealthiest can afford. that might sound good, but everyone in the country has to pay for wages. Even janitors have to pay the wages of the people who operate the checkouts at the local market or fix potholes in the local streets. If only the wealthiest can afford to pay for labour then the cost to janitors also increases. In a market with 100% employment the janitor will demand more money for his work, which means the street fixes and checkout chicks will demand more money and the whole thing spirals out of control.
Getting back to the OP, the optimal unemployment rate is controversial, but generally considered to be between 2% and 7%. It also varies depending on the flexibilty of the economy. In terms of economic change when there are large numbers of jobs being offered, a higher unemployment rate s generally optimal. In a static economy when there are few new jobs on offer, a lower rate is optimal.
Essentially you are aiming for an unemployment rate that reflects the people walking from one job to another, rather than people being laid off and not being able to find a job.