The rules for auto-cw are:
Posts enter community wiki mode when one of the following happens:
The body of the post has been edited by at least five (5) different users.
The post has been edited ten (10) times by the original owner.
[..]
[..]
[..]
The question generates more than 30 answers (15 on Super User, 60 on Code Golf). In this case, the question and all answers
will enter community mode, as will any future answers.
(removed conditions that explicitly make post CW, emphasis mine)
Remark ragarding condition 1: If more than 4 users actively contribute to a post it should be community wiki, as it is the result of many users collaborating. If most of these edits however are minor grammar/spelling edits, it should not. This must obviously decided depending on the situation.
The question is about condition 2; If users invest a lot of work into improving their own answer, toggling CW on the tenth edit (without warning!) serves to do exactly one thing: Discourage users from investing effort in improving their posts (specifically, their answers) as any further votes on the question do not count towards their rep. I don't think this makes a tremendous amount of sense, as improvements are welcome and people shouldn't be conditioned to avoid them.