How often should you use a heading? Are there any guidelines or limitations to using headings too often (i.e., every paragraph, every other paragraph, etc.)?
The correct but useless answer is: It depends.
But one could say: If every paragraph has a new heading, that's almost surely too much. It just becomes distracting.
If you have only two headings in a 600 page book, that's almost surely too little. It's of little help in breaking up the book or helping the reader find desired information.
In general, I avoid having more than one heading per page. If I find that I am putting two or three headings per page, I try to move the headings to a "higher level". For example, if I started out having separate headings for Brazil and Venezuela and Ecuador and France and Britain and Germany and so on, and I only had a paragraph or two for each country, I'd consider making headings for continents instead of countries.
If I have less than one heading for every ten or twenty pages, I'd do the reverse: make the headings at a lower level so that there are more of them.
In a short document, if I have only one or two headings for the whole document I'd break it up more. In general I try to have at least three or four headings.
But even these broad guidelines I would not advise anyone to follow slavishly.
One thing a heading does is allow you to concisely introduce a new section. I've had times when I've started out writing, "In the United States ..." and then two paragraphs later, "On the other hand, in Brazil ...", and then a few paragraphs later, "The situation in France, though, is ...". And after three or four of these I'm struggling between using the same words to introduce each section, and thus sounding repetitive, or trying to come up with fifty different ways to transition to another country. Putting in headings that say simply, "United States", "Brazil", "France", etc, solves the problem neatly. Even if there were too many of them, this is probably preferably to wrestling with how to say "here's the next country" fifty times. (BTW some writers get around this by not clearly identifying that they are now talking about a different country, or whatever the shift in subject is, which I think is a terrible solution, because now the reader has to figure it out.)
So to sum it up: If you have more than one or two headings per page, I'd THINK ABOUT ways to reduce the number of headings. But if you can't think of a way to do it without making the document harder to understand, don't worry about it.