FAQ Clean-up Note: This answer is meant to help clean up this FAQ by creating a canonical answer that sums up all the information available in the question and further explaining it. Please feel free to edit in pieces of information that are missing or unclear. Eventually, other answers will be deleted.
Copying and pasting the same answer to multiple questions can cause different reactions depending on what answer you're pasting. The acceptableness of this behavior ranges from "highly frowned upon" to "completely unacceptable" (note that it never reaches the "acceptable" end of that spectrum). If you catch yourself or someone else doing this, please evaluate the answer and see if there is a more correct thing to do.
Are the questions duplicates of each other?
Duplicate answers most often indicates that the questions are asking the same thing. If the questions could be considered duplicates of each other, only post the answer to the best one, will you think would make the better candidate for the other to point to. Flag or vote to close the other one so that it can be directed to the better question which has your answer. If you're spotting a duplicate answer to duplicate questions, flag or vote to close and then flag the answer on the duplicate question for removal (leave the other one alone).
Are they promotional in any way?
Duplicate answers across questions that promote external links or resources are considered astro-turfing and will likely result in the immediate deletion of all the answers involved. Most often, these answers get posted across questions which only hold some remote relevance to the link they're trying to throw out there. The answers often consist of little more than a vague explanation of what the link contains or what the tool does. Depending on the degree of astro-turfing and status of the account, a wide range of punishments could get issues, from a simple warning to account destruction.
Could the answers be more specific to each question?
If you've gotten past the other two questions, your answer may just be too vague. Answers that solve over-generalized problems are not as useful to questions - they should be tailored to address the specific needs that each question has outlined. If linking something, explain the relevant parts to the OP, or explain how the code or tool you've linked is relevant and useful to them. Don't just throw out answers thinking "this is relevant" - explain how it is relevant. It's not always so obvious.
The Community user will issue an automatic flag
Any time you post answers which are exact duplicates of each other, the Community user will automatically raise a flag that 10k users and moderators can see, in order to evaluate your answers based on the criteria we've outlined above. So please, before you get other users involved in your copy-pasting business, do the work yourself and you might be able to avoid bad situations in the first place.