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, &cetc.), 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.