This started as a discussion on chat and it grew into a larger discussion than I anticipated. I'm going to move it over here as suggested by Gung. Here are some links to allow others to follow the original discussion:
Based on the discussion in chat and here my understanding is:
Pleas for help should be removed as part of a larger edit, just like "Thanks", and <poster's name/signature>.
Smaller edits produce benefits (they make threads more readable for future readers, and set a better example of the site's standards and expectations for future posters) and costs (they clog up pages sorted by recency of activity (the home page, user's favourites, etc.), denying attention to more recent questions, or those with new answers or more substantial edits). The benefit/cost ratio is most advantageous if
A question has high visibility: on popular threads with thousands of views, an edit will benefit many future readers.
A question is freshly posted, or recently bumped to a high position on the front page: reduces the "costs", as an edit will not bump another thread from the activity page.
When activity on the site is slow: during busy times, questions fall off the front page very quickly and adding minor edits to the activity stream will only make this worse.
When you are editing only one or a couple of questions. If you have a large batch of edits you are working through (e.g. as part of a systematic re-tagging†), consider throttling your activity by only submitting a few at a time so you do not clog the front page.
In general when you edit, fix everything you can. If the only fix isn't going to make a worthwhile difference, then think twice, before editing.
† Which you should discuss here on Meta before embarking on.