One reason why this represents a challenge is that often a party’s stake in a business as a member (in the case of a close corporation) or a shareholder (in the case of a company) is proportionate to that party’s interest in the underlying legal entity. In other words a 50% member/shareholder often holds 50% of the equity and exercises an appropriate degree of influence over the business’ affairs. Notwithstanding the challenges, this approach seems more sustainable because it caters for changing circumstances which perhaps should, in turn, affect matters like how much equity the parties hold over time.
(Thanks to Matthew Buckland for the link)