How and when to remove the space on the left hand of the beginning of a paragraph?

Question

I have something like that:

\section{subsection}
...
\begin{figure}
...
\end{figure}
texttexttext
...

It turns out that it does not put the "texttexttext" on the very left hand side... it leaves some space... My questions are:

1. How to remove this space?

2. Generally speaking, in a technical report, when should we leave some space on the left hand side of the beginning of a paragraph? when shouldn't we?

3. If we leave some space the left hand side of the beginning of a paragraph, should we leave a blank line above it to separate from the previous paragraph?

4. Also, what is the best way to add a blank line? \\[1em]?

I would like to know the convention.

Answer 1

1. In answer to your first question, this space is 'provided' by \parindent and indents the paragraph by a certain amount. In order to remove it, prepend the paragraph with \noindent. Some more information on practical and not-so-practical global changes that affect \parindent, read the TeX FAQ entry on 'Zero paragraph indent'.

2. Your second question deals more about personal preference, since there are many documents I've seen that use either an indent or not. Regardless of the choice, even from a technical point of view, consistency should reign supreme.

3. LaTeX provides some guidelines as to where this indentation occurs or not. Some macros (like sectional commands, to name one) end using \noindent (and sometimes \ignorespacesafterend) to drop the indent from the paragraph following the command. Perhaps as a prime example, consider the titlesec package. Adjusting the spacing around sectional commands <command> is performed by means of

   \titlespacing[*]{<command>}{<left>}{<before-sep>}{<after-sep>}[right>]
   

The starred * version specifically kills the indentation of the paragraph following <command>. Again, with the choice left up to the user/typesetter, this could be considered personal preference.

4. In order to produce an empty line you could use

   ... orci velit, suscipit quis congue at, laoreet vitae elit.
   
   \mbox{}% Creates an empty box
   
   Lorem ipsum dolor sit amet, consectetur ...
   

   However, this will necessarily create an empty-line paragraph, and therefore have a \parskip above and below the line. Although the use of \\[<len>] works in text mode for paragraph spacing, is typically used in tabular and array environments. For vertical whitespace of a specific length, use \vspace*{<len>}. You will notice LaTeX complaining about Underfull \hbox (badness 10000) in paragraph at lines ... though, which should identify incorrect usage of spacing associated with line breaking.

Answer 2

Here are some answers to your questions.

The "space" you are referring to is the paragraph indent, and it is automatically added to each new paragraph (which in your LaTeX source is created by adding a blank line between pragraphs.) It may also be added automatically at the end of certain environments.

The default for most document classes is to indent every new paragraph except for those immediately following a chapter/section/subsection heading.

1. To remove the indent in a single paragraph, use the \noindent command. You shouldn't generally need to do this, however. If you find indented paragraphs after an environment (e.g. displayed math) that you don't need, you should make sure there is no blank line in your source after the environment. It's helpful to insert a % on a line by itself in these cases to make your source more readable.
2. When to break a paragraph and when not to is a writing question: it has no direct objective answer, although roughly a paragraph corresponds to a single idea. Here is a link to a reasonable explanation: Paragraphs and paragraphing.
3. If you are indenting new paragraphs, there is no need to insert blank lines in the output between paragraphs. (Of course your source document will use blank lines to separate paragraphs.)
4. In general, you shouldn't use \\ to create blank lines. The \\ command inserts a line break within a single paragraph. As Werner says in his answer, line spacing around headings should be done by the heading definition, and not manually. If you do need to make a blank line, on an exceptional basis, you can insert space with the \bigskip commands (or \vspace{}) command, or but generally you shouldn't have to do this. See What is an elegant way to insert a skip between two paragraphs?.

For some documents (not regular reports/articles/theses/books) it is sometimes appropriate to have no paragraph indentation, and separate paragraphs with blank lines. If you need this kind of format, you should use the parskip package.