Problems

But what about the negative effects of Unemployment?

It is not working for new industry!

Hey! My specialized industry just abandoned even with 4% unemployment!

I have high unemployment and no demand for anything!

Is not enough workers harmful?

Is this an optimal way to play?

As far as I can tell, you can have at least 15% unemployment with no observable harmful effects at all. At that point your population will tend to stop growing, but as you zone new employment opportunities immigration will very quickly resume. In order to get problematic levels of unemployment you'd have to do something extreme like dezoning all your workplaces, otherwise unemployment self-stabilizes by suppressing immigration.The advice of maintaining unemployment is really about preventing existing industry from abandoning and wont magically prevent all "not enough worker" zots. Cims are terribly reluctant to take industrial jobs (with the exception of lvl3 industry). However, theyIt just means you need to be patient when establishing new industry later in the game.Cims have quite high "inertia", they tend to stay in their current job - or state of unemployment. This means it is hard to establish new industry, but once established it should be reasonably robust.I also tend to find that it is easier to establish new industry when you have high influx (i.e. a lot of immigration), but industry will always establish itself eventually provided there are unemployed cims even if some of the buildings go through a couple of abandonment cycles before finally being established.This can happen due to what is called a Retirement Wave or a Young Adult Exodus Wave. It can be that all the workers are nearly the same age because they all immigrated or graduated at the same time as the specialized industry was looking for workers. Then they reach the next phase of their life and all leave the city or retire at the same time and suddenly the building has no workers. This is kind of hard to avoid completely, but if you zone the specialized industry incrementally over several years then only small portions will abandon at any one time. Otherwise just wait for the industry to find new employees.This could be related to traffic problems. Demand for commercial and industry depends to an extent on them being able to sell goods, if your transportation network is clogged up with a lot of delivery vans and trucks getting de-spawned then your existing industry and commercial won't be profitable and demand will fall.As far as I can tell it has no negative effects on the city morale. A building suffering from not enough workers still pays tax income and for most intents and purposes is the same as a properly functioning building and these buildings still stimulate residential demand and immigration just like "healthy" buildings do, making them a wonderful thing for rapid growth. While they eventually abandon this is normally of little concern for industry as industry hardly cares about land value and the abandoned building will soon be replaced with a new building.Not nessecarily, although I believe monitoring unemployment and the population view does improve one's game. It results in a residential-heavy city and residential is one of the poorer ways to make tax income, the cream of the city is generally commercial,office and lvl3 industry. The usual goal of employment stability is to enable specialized industry even in a mature city yet specialized industry itself is of dubious benefit - normally a combination of lvl3 Generic Industry and Industrial Space Planning to make imports go further is difficult to improve upon.Nevertheless any downsides are slight and near-absolute jobs stability is a nice thing to have so I would not hesitate to recommend this employment management strategy to any player, whether playing for flavor of to build an optimally running city.The exception is if you want to grow your city as fast as possible, in which case you should aggressively use up all demand immediately, while there will be rampant "not enough workers" the city will grow extremely fast, generate huge tax income and have no problems with death waves.