The full sentence reported in the privilege page is the following one:
Try to make the post substantively better when you edit, not just change a single character. Tiny, trivial edits are discouraged.
The sentence doesn't say that tiny, trivial edits are forbidden.
The sense of what the privilege page is trying to communicate is that, when you find a word that is misspelled (for example), you should also check if there is something else in the post that needs to be changed to make it better; if there is something else that needs to be changed, then you should change that as well, to avoid the need for somebody else to edit the post once again.
If you find the following text in a question, you should not just change the function name, but also change the punctuation used in the sentence.
i want, to use the Drupal function
load_user(). but it's does not return an object i, can use. any help, plaese?
That doesn't mean single character edits are forbidden; there are surely some cases where a misspelled word needs a single character edit, and where the word as it is written would cause the post to be misunderstood.
The only users who cannot make any single character edits are the users without the privilege of editing posts. The text reported in the privilege page is still valid for those users; the only difference is that for such users the suggestion to avoid single characters edit is forced.
The reason for having that reinforcement is that the edits made from the users who don't have the privilege to edit posts are suggestions that somebody else needs to review; rather than requiring users to review a proposed edit that should be rejected because is changing a single character, it is better to have an automatic checking that avoids those edits, and require a user's review for something less trivial. I can imagine that avoiding users get reputation for trivial editing a post is another reason to avoid single character edits from who doesn't have the privilege of editing any posts. (Between the two reasons, the latter is probably the less important one.)