I agree with SQLSister. Paragraphs can be a single sentence, but that sentence needs to function as both the topic and exposition. It may be, in some cases, that no exposition is required, but that requires assumption(s) about the knowledge level of the reader, which can be perfectly acceptable, such as assuming "common sense" (whatever that may be), but is still, nevertheless, an assumption.
As for a single word paragraph, that generally only makes sense in context because usually the subject of that sentence is implied, and can only be determined by context. It only works if it's aboslutely clear what is implied.
As said above, most people have problems by putting too much information in a paragraph by including irrelavent details, or off-topic information, which by the way, is known as paragraph sprawl.
Good Luck
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