Add a short paragraph / note at the start of https://drafts.csswg.org/css-rhythm/#line-height-step (perhaps move the property definition to a subheading / section parallel to the block box section) that summarizes the use-case(s) and notes limitations.

E.g. something like: (text taken from portions of an email by @fantasai )

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Normally an author can fairly easily ensure that, within a paragraph, the line height follows a strict vertical rhythm. As long as the text is not interrupted by atomic inline content or text that has a larger font size / different vertical alignment (the majority of text), it will maintain rhythm. For such interruptions however, use the line stepping properties to preserve rhythm.

Notes:

1. It is not clear that line height stepping is necessary
2. There are many issues with inline layout that need to be addressed before it can be an effective
   solution to the problems it addresses.

For text rhythm across paragraphs, headings, and blocks in general, see block height stepping, which will more directly solve most use cases.

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