The efficiency which resources distribute through market mechanics is optimal, either in the ex ante, interim or ex post.

市场机制配置资源的效率是最优的，无论从事前、事中还是事后效率。

youdao

The choice between an ex ante prohibition of certain conduct and an ex post, case-by-case review of complaints turns on the potential for efficiency justifications.

FORBES: Program Access Reform at the FCC: Are Exclusive Programming Deals a Good Thing?