Wikipedia:Not so arbitrary breaks

Sometimes a long discussion benefits from sectioning. Perhaps there's a shift from a threaded discussion to !votes, or a pronounced change in subject or focus. Sometimes editors will add a break randomly, typically labeled "arbitrary break." An explanation and rationale for such breaks is provided at Arbitrary section break.

Often, however, arbitrary breaks are not so arbitrary.

Not so arbitrarily highlighting one's own comments
A user adding an "arbitrary break" immediately above their own comments may be acting in good faith, but is ultimately just increasing attention to their own words by separating them from the rest of the discussion. Doing so has two functions: increasing visibility of one's own comments above others and, to a much lesser extent, setting the tone/subject for those that follow.

There are lots of very good reasons to create a sub-section for your comments. None of them are "arbitrary," though.

Not so arbitrarily highlighting someone else's comments
Similarly, a section heading inserted above a comment, question, bit of evidence, or !vote one finds particularly important or compelling is not arbitrary. It serves a clear organizational or rhetorical purpose, highlighting that comment by pulling it apart from those that came before it.

If you're adding focus to a particular point, perspective, or user in a rhetorically meaningful way, and are conscious of doing so, it's not arbitrary.

If you suspect that someone is adding a not-so-arbitrary break, remember to assume good faith and first consider whether the break might serve to mark the mid-point of an existing section, the most recent tangent, or some other non-rhetorical function before making an accusation.

Sometimes a unique heading is the way to go
If you'd like to break up the text for organizational/readability reasons and a purely arbitrary break doesn't seem like the way to go, maybe a unique heading would help. At very least, it avoids duplication of the heading "arbitrary break", which can commonly happen on long discussion pages.