Here's how I see it. There are a few situations.

 1. __Exact Duplicate__

  - If the questions are asking the same thing, and you see one question has a proper solution, then it would be better to use the duplicate flag rather than clone the answer.

  - When you flag, users with at least 3,000 reputation will see the flag in one of the review queues and vote to close it as a dupe. Once you reach 3k, you'll be able to directly close questions (they will still go into Review, as 5 votes are needed).

 2.  __Same Solution__

  - There's been discussion about the "lazy dupe," where people close one question as a dupe of another, just because they have the same solution. It's not a true dupe, and other users are annoyed at this behavior.

  - If you find the solution to the question on another Ask Ubuntu Q&A _that is not a dupe_, then the best practice is usually to phrase the answer in your own words and include a link to the original. A link-only answer should be avoided, as those are generally flagged and deleted.

 3. __Similar Solution__

  - This one could probably go without saying, but I'll put it in for clarity's sake.

  - If you find an answer on AU that _could_ apply to the question you're dealing with, but isn't an exact solution, then adapt the answer in your own words and include a link.

  - For example, [my answer about remapping capslock](https://askubuntu.com/questions/82837/how-do-i-make-the-caps-lock-key-a-third-shift-key/819356#819356) is very closely adapted from a more general answer for a question about making `xmodmap` permanent. The question isn't the same at all, but the answer follows the same theme as the question I was researching.