The expression was formed to make "unskilled labour" more effective. Around the 60ties and 70ties when skilled labour was short in central Europe's manufacturing plants, unskilled labour from the South of Europe was recruited, sometimes from rathr backwards regions, i.e. People could hardly read or write. After a period of painful training, they could do certain tasks, use or clean or service certain machines etc. It was then found, that more effeciency could got out of these people when employers took the pain + cost to teach them several skills: Increased awareness, pride in the job well done and new tasks achieved, enhanced turnout and quotas of failure as well as working accidents sunk drastically. It also made staff allocation more flexible. Today- changing application of non-or semi-skilled labour is a routine to avoid boredom of the employee and lack of awareness. Multi-skilling is also applied to skilled labour today, and especially US-companies also apply it on academic trainees – there it is commonly called job-roation. By understanding the defined goals of several departments within a company, the future manager gets a better understanding of the total process, the key-people involved etc.
