You lock up your capital until retirement, but it is protected from double taxation.

FORBES: The Perverse Impact Of Double Taxation: A Helpful Flow Chart

The stakes lock up a company's capital and it is hard to claim they spread risk.

ECONOMIST: Japanese business

In this decade, private-equity fund managers have gathered billions even though investors who back such funds have to lock their capital away for up to ten years.

ECONOMIST: The rights of shareholders and the wrongs done to clients