The division of labour is a
bipolaric thing. It is the
source of
wealth but on the other hand it's also the source of
alienation.
The division of labour enables people to specialize on certain things -- an occupation really comes a profession. Some people are more effective than others on certain things and they can exchange services creating more wealth (or create it in shorter time). There are thousands and thousands different jobs to do and it should be obvious that no one can master all of them. Therefore people are more and more interconnected and dependant on each others. This dependancy is highlighted every time when there's a strike.
If the division of labour was introduced in positive sense by Adam Smith, Karl Marx was one of them who offered a negative viewpoint. The division of labour is the most important concept in German Ideology. Marx claimed that the prevailing division of labour defines the prevailing relations of possession. For Marx communism meaned the end for the division of labour and thus work becomes spontaneous joy. A worker isn't just an extension of machine anymore but the work becomes the process of self-improvement.
All this is to say that a worker loses all interest in work if she is involved in the working process only by the tiny, specialized amount. A worker is alienated from final product and from the work itself as well. The work is nothing but the mean to earn money for her.
(We can again note that this is yet another Marx's concept that clashes with the official truth of soviet-communism..)