This decision is entirely up to you. Making a post community wiki will result in the following:
- A much lower reputation (100 instead of 2000) is needed to edit a community wiki post.
- Voting on a community wiki post (up or down) does not affect any user's reputation.
This might make it easier for others to edit your answer, because it's now community-owned, and they don't feel they're changing your answer.
There are no "criteria" for you to decide whether you need to make something community wiki. You never have to. However, if you specifically want others to continue improving your answer, then by all means, make it community wiki, and leave a note for others to see. This would encourage contributions.
Note: I've made this CW myself, so we have a practial example :)