Questions have functionality for opening posters to select one more more 'Accepted answers'.
A member who replies may 'Suggest an answer'.
Discussions are open ended and do not have this functionality.
Selecting 'Suggest as answer' on a reply notifies the opening poster that you think your answer will solve their problem. The opening poster may then choose to accept or reject that answer. An opening poster may accept any answer, regardless of if it has been suggested.
'Accepted answers' are a user-centric way of identifying that a question has been answered to the opening poster's satisfaction.
If a member has posted a suitable answer that has helped solve their problem, then they should select Accept answer on the post that helped. This means that the answering member knows the value of their answer and lets future readers know which has help you find your answer.