There is a lot of financial engineering that goes into situations like this and you have to look into it on a case by case basis. But often times investing in spinoff companies can be very profitable. In fact spinoff companies outperform the overall stock market - you can checkout the Bloomberg Spinoff Index.
The book How to be a Stock Market Genius covers situations like this and gives some tools to analyze them if you are interested in learning more about it.
Large conglomerates like IBM usually trade their shares at a discount because they're poorly managed due to the sprawling size. Breaking businesses with little synergies usually makes the separate pieces better managed and thus more valuable.
The book How to be a Stock Market Genius covers situations like this and gives some tools to analyze them if you are interested in learning more about it.