Long emails, long sentences, long excuses and long explanations. Eventually your audience will get bored of them. I have in the past been extremely guilty of that. Partly, I'd say, because of the traditional writing culture in Portugal. There is an abundance of asides and inclusions in speech with parentheses and commas.
But it's a bad habit.
How short is short enough? Apparently, your short term memory can reliably relate up to 7 chunks of information at a time . And so, each sentence should contain no more than 7 relevant elements, including subject, object, verb, adverb. And you should intertwine up to seven sentences in a syntactical paragraph or seven propositions in a logic argument.
I am trying hard to keep myself under 7 chunks.