I say that each person should get credit (or critique) for their own answers. If someone has another method for the same task, they should make their own answer.
Put this example:
Someone adds a method to an answer which is plain wrong. The OP will receive downvotes for that wrong part of it's answer. The same backwards, it would receive upvotes for giving a complete answer.
SO, SU, and U&L have several questions where there are several methods to complete a task, and each user makes their own answer. If OP (answerer) discover another method, he should add it to his own answer, etc. If you are a new user, you should prefer making your own answers, since:
- Editing other answer only gets you 2 rep, while your own answer could get you from 10 onwards reputation.
- Your edit can be rejected as "This edit changes too much in the original post; the original meaning or intent of the post would be lost" since your edit actually is too extensive and maybe the answerer didn't like it.
- You should get credit (critique) for your own answers. Is all the process of being better with time.
TL;dr: Each person with their own answers. Unless is correcting a mistake of the already stablished answer you shouldn't edit someones answer and instead answer it yourself.
Little example, as you can see he added his own answer instead.