avail、benefit与profit这些动词均含有“有益于、有益”之意。

avail ：较文雅，常见于历史小说、演说或讲道中，较少用于日常话语，侧重功效或效力。

• Of what avail is it?
  何济于事？
• His efforts were to no avail
  他徒劳无功。
• I apologized repeatedly, but to little avail.
  我一再道歉，但丝毫没有奏效。
• I avail myself of this opportunity to renew to you the assurances of my highest consideration.
  顺致最崇高的敬意。
• Now it's done, regrets are of no avail.; It's no use crying over spilt milk.
  事已如此，后悔也是枉然。

benefit ：通常既可指个人情况（如身体、智力或精神状态等）的好转或改善，又可指对实现某个目标等带来的好处。

• We should spend the money on something that will benefit everyone.
  我们应该把这笔钱花在大家都能得益的事上。
• Both sides have benefited from the talks.
  双方都从谈判中获益。

profit ：着重于物质方面的受益，常用于财富或知识等方面的得益。

• Farmers are profiting from the new legislation.
  新法规使农民受益。
• We tried to profit by our mistakes (= learn from them).
  我们努力从错误中吸取教训。
• Many local people believe the development will profit them.
  当地的许多人认为，这项开发将对他们有利。