they do not allow re-use;

它们不允许重用；

Don't strain to re-use code; reorganize instead.

不要过度重用代码，而是通过重新整理代码来完成重用。

That wouldn't allow them to re-use the plan, right?

那么他们将没法复用这个方案，对吗？

Services can (and should) also re-use existing services.

服务也可以(也应该)重用已存在的服务。

So what's so challenging about exposing a service for re-use?

那么，为了重用而公开一个服务为何如此具有挑战性呢？