I would advocate for each answer being posted separately for two reasons:
- Combined answers may contain one good and one bad answer. In those cases, both voters and the OP may be conflicted in designating their votes (or acceptances), since upvoting an answer may be an endorsement of the bad answer, and downvoting a good answer is "throwing the baby out with the bath water". This lack of precision may serve to detract from participation.
- Combined answers may offer two separate good answers. If there are two good answers, the voting by the community can help discern the best of two good options. By combining the answers, this handicaps the Questioner from the benefits of the community input, in an important way.
Unless we are considering a very strict institutionalization of 1 answer per submission, and 1 submission per user, or some modification to the voting process - both of which I would be disinclined to do - we should advocate for 1 answer per submission, and support users to make multiple submissions.