Why should I put a ~ before \ref or \cite?

Question

My question is in the title of this post, but extends to other referencing commands like \eqref, \citep, \citet (and the like) as well.

Answer 1

The ~ is a non-breaking space, (not really a symbol) so when you write in your text Table~\ref{mytable} it ensures that the Table part is kept together with the number. This is generally considered to be good for readability.

So that you don't forget, it's often helpful to make macros for references like these:

\newcommand*{\tabref}[1]{\tablename~\ref{#1}}
\newcommand*{\figref}[1]{\figurename~\ref{#1}}

Then you use \tabref{mytable} and \figref{myfig} in your text.

The refstyle package provides a generalised interface to automatically construct macros like those above.

The cleveref package with its \cref command is even more powerful, since it figures out what type of object your reference refers to and generates the correct text automatically (so you don't need different \ref commands for different reference types.)

If you are independently using the hyperref package, it also provides an \autoref command that works like cleveref's \cref command (and also makes the hyperlink target larger.)

Answer 2

The ~ is called a tie because it ties two words together like in Section~\ref{sec:intro}. The tie causes TeX never to break a line at a tie. Hence, Section and the reference will end up together on the same line, making them easy to read. Tying together what belongs together is good practice and is not limited to \ref. Another good use is tying an academic title to a name.