Attribution of material goes without saying. Incorporation of material is fine as long as you have a good reason to do so.
Compilation answers are often valuable - but some questions just don't need them. It depends on factors such as how many answers there are or whether any ideas are fragmented between answers.
In a non-compilation answer, try to avoid duplication. If you think an idea needs to be highlighted, you can mention that someone else's answer explains the idea and mention how it fits in with your answer. Sometimes, though, another answer's exploration of the idea will be insufficient and it is better to just cover everything yourself.
In summary: its fine, but think about what you are doing