Which business document is usually written in block style with the body text aligned along its left margin?

It just depends. Like a modified block letter, all the paragraphs line up at the left margin. You do not need to indent at all. And in a semi-modified block letter, all the paragraphs line up at the left margin. However, the first word in each paragraph is indented. Or could be a block letter, all the paragraphs line up at the left margin. There is no indenting of the paragraphs. Hope this helps!