Where and how is "Alternative Spelling" used?
One answer
I use it to "hold" abbreviations, acronyms, and plural versions of the terms, so that a search on any of those will find the term.
Comments
How would synonyms differ in this regard?
Synonyms might not differ -- it depends on how you want to treat them. You could treat them like abbreviation (including synonyms as alternate spellings). Or you could define them separately and in their definitions include something like "see also <the-other-term>"