Some unemployment is normal. People find work in your own facilities, and in the private economy. Private economy demand for workers depends on the needs of your colony not taken care of by yourself, i.e. doctors, teachers, security and entertainment. Many people not finding work in these sectors will look for entrepreneurial opportunities, which is heavily dependent on their education.

Low unemployment can signal a labor shortage and your buildings may not be fully staffed. Remember that on average, 2/3rd of your population are of working age, and neither the sick nor criminals contribute.

High unemployment is often a sign of low education with too few people qualified for private economy jobs.