It's usually about "shareholder value". In other words, the two new companies will be worth more (on Wall Street) than the old company. In HP's case, the idea

It's usually about "shareholder value". In other words, the two new companies will be worth more (on Wall Street) than the old company. In HP's case, the idea was that the shares in the enterprise company were depressed by worries about the viability of the PC/printer company. In Yahoo's case, the problem is that Yahoo's core business has little or no value (ie it's not reflected in the price of the shares) compared with the value of its shareholdings in Alibaba and Yahoo Japan. In Google's case, it's currently just re-arranging deckchairs. However, the underlying problem is that Google's share price reflects Google Search, and does not reflect all the other businesses that now come under the Alphabet umbrella.