Originally Posted by wizwor
You buy back stock when you feel that the return on the stock repurchased is greater than what it would be to invest otherwise.
That is one reason why Dell and the BEST BUY founder are taking their companies private; they consider the stock to be undervaed and that they can reengineer the company for future growth that will make it more valuable. Later they can refloat the company and rake in big bucks then.
Buy low, sell high.
(Strictly-speaking it is a form of "insider trading", but a legal one since it is based on public data and personal opinion.